DESERTIFICATION
Desertification is the degradation of once-productive land into unproductive or poorly productive land. Since the first great urban-agricultural centers in Mesopotamia nearly 6,000 years ago, human activity has had a destructive impact on soil quality, leading to gradual desertification in virtually every area of the world.
It is a common misconception that desertification is caused by droughts. Although drought does make land more vulnerable, well-managed land can survive  droughts  and recover, even in  arid  regions.  Another mistaken belief is that the process occurs only along the edges of deserts. In fact, it may take place in any arid or semiarid region, especially where poor land management is practiced. Most vulnerable, however, are the transitional zones between deserts and arable land; wherever human activity  leads  to  land  abuse  in  these fragile marginal areas, soil destruction is inevitable.
[1] Agriculture and overgrazing are the two major sources of desertification. [2] Large-scale farming requires extensive irrigation, which ultimately  destroys  lands  by depleting its nutrients and leaching minerals into the topsoil. [3] Grazing is especially destructive to land because, in addition to depleting cover vegetation, herds of grazing mammals also trample the fine organic particles of the topsoil, leading to soil compaction and
erosion. [4] It takes about 500 years for the earth to build up 3 centimeters of topsoil. However, cattle ranching and agriculture can deplete as much as 2 to 3 centimeters of topsoil every 25 years - 60 to 80 times faster than it can be replaced by nature.
Salination is a type  of  land  degradation that  involves  an  increase  in  the  salt content of the soil. This usually occurs as a result of improper irrigation practices. The greatest Mesopotamian empires- Sumer, Akkad and Babylon- were built on the surplus of the enormously productive soil of the ancient Tigris- Euphrates alluvial plain. After nearly a thousand years of intensive cultivation, land quality was  in  evident  decline.  In response, around 2800 BC the Sumerians began digging the huge Tigris-Euphrates canal system to irrigate the exhausted soil. A temporary gain in crop yield was achieved in this way, but over-irrigation was to have serious and unforeseen consequences. From as early as 2400 BC we find Sumerian documents referring to salinization as a soil problem. It is believed that the fall of the Akkadian Empire around 2150 BC may have been due to a catastrophic failure in land productivity; the soil was literally turned into salt. Even today, four thousand years later,  vast  tracks  of  salinized land between the Tigris and Euphrates rivers still resemble rock-hard fields of snow.
Soil erosion is another  form  of  desertification.  It is a self reinforcing  process; once the cycle of degradation begins, conditions are set for continual deterioration. As the vegetative cover begins to disappear, soil becomes more vulnerable to raindrop impact. Water runs off instead of soaking in to provide moisture for plans. This further diminishes plan cover by leaching away nutrients from the soil. As soil quality declines and runoff is increased, floods become more frequent and more severe. Flooding washes away topsoil, the thin, rich, uppermost layer of the earth’s soil, and leaves finer underlying particles more vulnerable to wind erosion. Topsoil contains the earth’s greatest concentration of organic matter and microorganisms, and is where most of the earth’s land-based biological activity occurs. Without this fragile coat of nutrient-laden material, plan life cannot exist. An extreme case of its erosion is found in the Sahel, a transitional zone between the Sahara Desert

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The pain of a migraine headache can virtually disable a person who suffers from it. Millions and millions of people suffer from migraines, although many of them do not even recognize that a migraine is different from a regular headache. A migraine is not at all the same as a normal headache, and it seems to have a very physical cause.
One symptom of a migraine is a precursor, which is a visual aura before an attack. Yet only about a third of patients actually experience that, and it is therefore not a requirement in the diagnosis. Other symptoms include increased pain when a person moves, nausea, and sensitivity to light and sound. Scientists now believe that migraines are caused, not by abnormal blood vessels as previously believed, but instead by a unique electrical disorder of brain cells. Physicians used to treat migraines with medicine to constrict blood vessels because of the belief that dilated blood vessels were the cause.
The new research has been enhanced by imaging devices that allow scientists to watch patients' brains during an attack. The results show that sufferers have abnormally excitable neurons, or brain nerve cells. Prior to the attack, the neurons suddenly fire off electrical pulses at the back of the brain, which ripple like waves on a lake after a stone hits the water. They ripple across the top and then the back of the brain, ultimately affecting the brain stem where the pain centers are located. The pain then generates possibly from the brain stem itself or from blood vessels inflamed by the rapidly changing blood flow, or perhaps from both.
Scientists have experimented by applying a powerful magnet to stimulate the neurons and discovered that some people's brains react differently than others'. When stimulation was applied to the brains of people who had suffered migraines, they saw the initial aura, and some actually suffered migraines. When the same stimulation was applied to the brains of people who had never suffered migraines, they realized no effect and the neurons showed no change.
Scientists and doctors continue to work on the research in an attempt to find the perfect treatment. It is considered important to treat migraines because it is believed that prolonged untreated attacks could cause physical changes in the brain leading to chronic pain.

The word enhanced in paragraph 4 is closest in meaning to

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Between 1945 and 1973, the economies of the industrialized nations of Western Europe, Japan, and the U. S. grew fast enough to vastly improve living standards for their residents. A similarly favorable growth was registered by some, but far from all, of the developing or industrializing nations, in particular such thriving Southeast Asian economies as Taiwan, Hong Kong, Singapore, and South Korea. After the devastation of World War II, a substantial rebuilding boom, combined with lavish flows of aid from the US, generated rapid growth in Western Europe and Japan. American multinational corporations invested heavily in the rest of the world. Perhaps the most important of all, energy was plentiful and cheap.

Poor nations need aid from the rich nations in the form of capital and of technological and organizational expertise. They also need easy access to the markets of the industrialized nations for their manufactures and raw materials. However, the political capacity of rich nations to respond to these needs depends greatly on their own success in coping with inflation and unemployment. In democratic communities, it is exceedingly difficult to generate public support for assistance to foreign countries when average wage earners are themselves under serious financial pressure. It is not easier politically to permit cheap foreign merchandise and materials to freely enter American and European markets when they are viewed as the cause of unemployment among domestic workers.

Japan carried out industrialization before World War II.

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In Viet Nam festivals often take place during the three months in spring and in autumn when people have a lot of leisure time. In addition, the climate in spring and autumn is especially suitable for holding festivals and for festivals goers to enjoy. Traditional festivals constitute a form of cultural activities, a spiritual product which the people have created and developed during the course of history. From generation to generation, the Vietnamese people preserve the fine tradition of “remembering the source while drinking water.” Festivals are events which represent this tradition of the community as well as honour the holy figures named as “gods” -the real persons in national history or legendary persons. The images of gods converge the noble characteristics of mankind. They are national heroes who fought against foreign invaders, reclaimed new lands, treated people, fought against natural calamities, or those legendary characters who affect the earthly life.
Accordingly, first and foremost, festivals are events when people pay tribute to divinities that rendered merits to the community and the nation. These are occasions when people come back to either their natural or national roots, which form a sacred part in their mind. Furthermore, testivals represent the strength of the commune or village, the local region or even the whole nation. Worshipping the same god, the people unite in solidarity to overcome difficulties, striving for a happy and wealthy life.
Moreover, festivals display the demand for creativity and enjoyment of spiritual and material cultural values of all social strata. They become a form of education under which fine traditional moral values can be handed from one generation to the next in a unique way of combining spiritual characters with competition and entertainment games. Festivals are also the time people can express their sadness and worries in a wish that gods might bestow favour on them to help them strive for a better life.

What does the author mean by saying “remembering the source while drinking water”?

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Twenty-five students from Walling School are currently living in France. They are there for three months as part of a living-abroad project. The 16- and 17-year-old students are living with French families and attending a French school. Most of the students have taken French language classes for 3 or 4 years and are finally getting an opportunity to use their French.
Not only are students learning a new language, but they are learning about a new culture, too. Students have been particularly surprised about the French attitude towards food. “They won’t leave anything on their plate,” says Vanessa Athol. “They aren’t wasteful at all.” Vanessa has vowed to be more careful with waste when returning to the United States.
The group’s chaperone, Mrs. Smith, has been pleased with the students’ acquisition of language. “Even the most timid are trying their best to speak. The students are learning a lot. I’m very impressed,” she said. Mrs. Smith added that she thinks living with a French family makes a difference because students are forced to speak French. “We are all very grateful to the French families who are hosting us.”
The French families are happy to have the students, as they are getting to leam about American culture. Both groups will be celebrating the exchange at a large potluck dinner at the end of the stay. There will be a slide show of memories and the students will speak about their experiences. Currently, the American students are periodically posting pictures and student essays on the Walling School website. “Living in France is an experience I’ll never forget,” writes student Tina Davis. “I know I’ll want to eat these croissants and this Camembert for the rest of my life!”

According to the passage, how will the students conclude their stay?

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Perhaps better known than the Cullinan Diamond is the Hope Diamond, a valuable and blue gem with a background of more than 300 years as a world traveler.The 112-carat blue stone later became the Hope Diamond was mined in India sometime before the middle of the seventeenth century and was first known to be owned by Shah Jahan, who built the Taj Mahal in memory of his beloved wife. From India, the celebrated blue stone has changed hands often, moving from location to location in distant corners of the world.
In the middle of the seventeenth century, a trader from France named Jean Baptiste Tavernier acquired the large blue diamond, which was rumored to have been illegally removed from a temple Tavemier returned to France with the big blue gem, where the stone was purchased by the Sun King Louis XIV. Louis XIV had it cut down from 112 to 67 carats to make its shape symmetrical and to maximize its sparkle. The newly cut diamond, still huge by any standards, was passed down through the royal family of France, until it arrived in the hands of Louis XVI and Marie Antoinette.
During the French Revolution, Louis XVI and his wife met their fate on the guillotine in 1793, and the big blue diamond disappeared from public sight.
The diamond somehow managed to get from France to England, where banker Henry Hope purchased it from a gem dealer early in the nineteenth century. The huge blue stone was cut into a 45.5-carat oval, and at this point it took on the name by which it is known today. The diamond stayed in the Hope family for around a century, when deep indebtedness brought on by a serious gambling habit on the part of one of Henry Hope's heirs forced the sale of the diamond.
From England, the Hope Diamond may have made its way into the hands of the Sultan of Turkey; whatever route it took to get there, it eventually went on to the United States when American Evelyn Walsh McLean purchased it in 1911. Mrs.
McLean certainly enjoyed showing the diamond off guests in her home were sometimes astounded to notice the huge stone embellishing the neck of Mrs. McLean’s Great Dane as the huge pet trotted around the grounds of her Washington, D.C. home. The Hope Diamond later became the property of jeweler Harry Winston, who presented the stunning 45.5- carat piece to the Smithsonian in 1958. The Hope Diamond is now taking a well-earned rest following its rigorous travel itinerary and is on display at the Smithsonian Institution in Washington, D.C., where it has been since 1958.

The pronoun "it" in the passage refers to

Read the passage below and decide whether the statements are TRUE or FALSE?

   Autonomous weapons are artificial intelligence systems that are programmed to kill. In the hands of the wrong person, these weapons could easily cause mass casualties. Moreover, an AI arms race could inadvertently lead to an AI war that also results in mass casualties. To avoid being thwarted by the enemy, these weapons would be designed to be extremely difficult to simply “turn off,” so humans could plausibly lose control of such a situation. This risk is one that’s present even with narrow AI, but grows as levels of AI intelligence and autonomy increase.

An AI arms race could inadvertently lead to an AI war

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George Washington Carver showed that plant life was more than just food for animals and humans. Carver’s first step was to analyze plant parts to find out what they were made of. He then combined these simpler isolated substances with other substances to create new products.
The branch of chemistry that studies and finds ways to use raw materials from farm products to make industrial products is called chemurgy. Carver was one of the first and greatest chemurgists of all time. Today the science of chemurgy is better known as the science of synthetics. Each day people depend on and use synthetic materials made from raw materials. All his life Carver battled against the disposal of waste materials and warned of the growing need to develop substitutes for the natural substances being used up by humans.
Carver never cared about getting credit for the new products he created. He never tried to patent his discoveries or get wealthy from them. He turned down many offers to leave Tuskegee Institute to become a rich scientist in private industry. Thomas Edison, inventor of the electric light, offered him a laboratory in Detroit to carry out food research. When the United States government made him a collaborator in the Mycology and Plant Disease Survey of the Department of Agriculture, he accepted the position with the understanding that he wouldn’t have to leave Tuskegee. As an authority on plant diseases – especially of the fungus variety – Carver sent hundreds of specimens to the United States Department of Agriculture. At the peak of his career, Carver’s fame and influence were known on every continent.

Why does the author mention Thomas Edison’s offer to Carver?

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The New York Times is a daily newspaper published in New York city. For a long time, it has been the newspaper of record in the United States and one of the world’s great newspapers. Its strength is in its editorial excellence; it has never been the largest newspaper in terms of circulation.
The Times was established in 1851 as a penny paper whose editors wanted to report the news in a
restrained and objective fashion. It enjoyed early success as its editors set a pattern for the future by appealing to a cultured, intellectual readership instead of a mass audience. However, in the late nineteenth century, it came into competition with more popular, colorful, if not lurid, newspapers in New York City. Despite price increases, the Times was losing $1,000 a week when Adolph Simon Ochs bought it in 1896. Ochs built the Times into an internationally respected daily. He hired Carr Van Anda as editor. Van  Anda placed greater stress than ever on full reporting of the news of the day, and his reporters maintained and emphasized existing good coverage of international news. The management of the paper decided to eliminate fiction from the paper, added a Sunday magazine section, and reduced the paper’s price back to a penny. In April 1912, the paper took many risks to report every aspect of the sinking of the Titanic. This greatly enhanced its prestige, and in its coverage of two world wars, the Times continued to enhance its
reputation for excellence in world news.
In 1971, the Times was given a copy of the so–called “Pentagon Papers,” a secret government study of U.S. involvement in the Vietnam War. When it published the report, it became involved in several awsuits. The U.S. Supreme Court found that the publication was protected by the freedom–of–thepress clause in the First Amendment of the U.S. Constitution. Later in the 1970s, the paper, under Adolph Ochs’s grandson, Arthur Ochs Sulzberger, introduced sweeping changes in the organization of the newspaper and its staff and brought out a national edition transmitted by satellite to regional printing plants.

To improve its circulation, the management of the Times did all of the following EXCEPT_.

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Choosing clothes can be difficult. Some people want to be fashionable, but they don’t want to look exactly like everybody else. Not all clothes are (1)........ for work or school, perhaps because they are not formal enough, or simply not comfortable. It is easy to buy the (2).......... size, and find that your trousers are too tight, especially if you are a little bit overweight. Very (3)........clothes make you feel slim, but when they have shrunk in the washing machine, then you have the same problem! If you buy light cotton clothes, then they might not be (4)........ enough for winter. If your shoes are not waterproof and if you aren’t (5)....... for the cold, you might look good, but feel terrible!
(3).................................

Choose the best answer:
When another old cave is discovered in the south of France, it is not usually news. Rather, it is an ordinary event. Such discoveries are so frequent these days that hardly anybody pays heed to them. However, when the Lascaux cave complex was discovered in 1940, the world was amazed. Painted directly on its walls were hundreds of scenes showing how people lived thousands of years ago. The scenes show people hunting animals, such as bison or wild cats. Other images depict birds and, most noticeably, horses, which appear in more than 300 wall images, by far outnumbering all other animals.
Early artists drawing these animals accomplished a monumental and difficult task. “They” did not limit themselves to the easily accessible walls but carried their painting materials to spaces that required climbing steep walls or crawling into narrow passages in the Lascaux complex.
Unfortunately, the paintings have been exposed to the destructive action of water and temperature changes, which easily wear the images away. Because the Lascaux caves have many entrances, air movement has also damaged the images inside. Although they are not out in the open air, where natural light would have destroyed them long ago, many of the images have deteriorated and are barely recognizable. To prevent further damage, the site was closed to tourists in 1963, 23 years after it was discovered.
1. In line 12, the word “They” refers to ………………...
 

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Public holidays in the United Kingdom, commonly referred to as bank holidays, are days where most businesses and non – essential services are closed although an increasing number of retail businesses (especially the larger ones) do open on some of the public holidays. There are restrictions on trading on Sundays and Christmas Day. Four public holidays are common to all countries of the United Kingdom. These are: New Year's Day, the first Monday in May, Christmas Day, and Boxing Day. Some banks open on some bank holidays. In Scotland, while New Year's Day and Christmas Day are national holidays, other bank holidays are not necessarily public holidays, since the Scots instead observe traditional local customs and practice for their public holidays. In Northern Ireland, once again, bank holidays other than New Year's
Day and Christmas Day are not necessarily public holidays. Good Friday and Christmas Day are common law holidays, except in Scotland, where they are bank holidays. In Scotland the holiday on 1 January (or 2 January if 1 January is Sunday) is statutory, and 25 December is also a statutory holiday (or 26 December if Christmas Day falls on a Sunday). Boxing Day is a holiday traditionally celebrated  the day following Christmas Day, when servants and tradesmen would receive gifts, known as a "Christmas box", from their bosses or employers. Today, Boxing Day is the bank holiday that generally takes place on 26 December. And 28 December only is given if Boxing Day is Saturday.
Like Denmark, the United Kingdom has no national day holiday marked or celebrated for its formal founding date. Increasingly, there are calls for public holidays on the patron saints' days in England, Scotland and Wales. An online petition sent to the Prime Minister received 11,000 signatures for a public holiday in Wales on St. David's Day; the Scottish Parliament has passed a bill creating a public holiday  on St. Andrew's Day although it must be taken in place of another public holiday; campaigners in England are calling for a bank holiday on St. George's Day; and in Cornwall, there are calls for a public holiday on St. Piran's Day.

The word “calls” in paragraph 2 is closest in meaning to     .

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In Viet Nam festivals often take place during the three months in spring and in autumn when people have a lot of leisure time. In addition, the climate in spring and autumn is especially suitable for holding festivals and for festivals goers to enjoy. Traditional festivals constitute a form of cultural activities, a spiritual product which the people have created and developed during the course of history. From generation to generation, the Vietnamese people preserve the fine tradition of “remembering the source while drinking water.” Festivals are events which represent this tradition of the community as well as honour the holy figures named as “gods” -the real persons in national history or legendary persons. The images of gods converge the noble characteristics of mankind. They are national heroes who fought against foreign invaders, reclaimed new lands, treated people, fought against natural calamities, or those legendary characters who affect the earthly life.
Accordingly, first and foremost, festivals are events when people pay tribute to divinities that rendered merits to the community and the nation. These are occasions when people come back to either their natural or national roots, which form a sacred part in their mind. Furthermore, testivals represent the strength of the commune or village, the local region or even the whole nation. Worshipping the same god, the people unite in solidarity to overcome difficulties, striving for a happy and wealthy life.
Moreover, festivals display the demand for creativity and enjoyment of spiritual and material cultural values of all social strata. They become a form of education under which fine traditional moral values can be handed from one generation to the next in a unique way of combining spiritual characters with competition and entertainment games. Festivals are also the time people can express their sadness and worries in a wish that gods might bestow favour on them to help them strive for a better life.a

Which of the following is NOT mentioned as a value of festivals?

The initial contact between American Indians and European settlers usually involved trade, whereby Indians acquired tools and firearms and the Europeans obtained furs. These initial events usually pitted Indian tribes against each other as they competed for the European trade and for the lands containing fur-producing animals. When the furs had been depleted, the Europeans began a campaign to obtain the lands the Indians occupied. The Indians often formed confederations and alliances to fight back the Europeans; however, the Indians’ involvement in the white people’s wars usually disrupted these confederations. Indians resisted the attempts by the whites to displace them. They fought defensive wars such as the Black Hawk War in 1832. Indian uprisings also occurred, like the Sioux uprising in the 1860s.
Despite the resistance of the Indians, the Europeans were destined to win the conflict. After Indian resistance was crushed, the whites legitimized the taking of Indian lands by proposing treaties, frequently offering gifts to Indian chiefs to get them sign the treaties. Once an Indian group had signed a treaty, the whites proceeded to remove them from their land. Often the Indians were forced west of the Mississippi into Indian Territory-land the whites considered uninhabitable. If only a few Indians remained after the conquest, they were often absorbed by local tribes or forced onto reservations.
No aspect of American history is more poignant than the accounts of the forced removal of Indians across the continent. As white settlers migrated farther west, Indians were forced to sign new treaties giving up the lands earlier treaties had promised them. Some Indian tribes, realizing the futility of resistance, accepted their fate and moved westward without force. The Winnebagos, who offered little resistance, were shifted from place to place between 1829 and 1866. About half of them perished during their perpetual sojourn. Other tribes, however, bitterly resisted. The Seminoles signed a treaty in 1832 but violently resisted removal. Hostilities broke out in 1835 and continued for seven years. The United States government lost nearly 1,500 men and spent over $50 million in its attempts to crush Seminole resistance. Most of Seminoles were eventually forced to Indian Territory. However, several hundred remained in the Florida Everglades, where their descendants live today.

What does the passage mainly discuss?

For a time, the Hubble telescope was the brunt of jokes and subject to the wrath of those who believed the U.S government had spent too much money on space projects that served no valid purpose. The Hubble was sent into orbit with a satellite by the Space Shuttle Discovery in 1990 amid huge hype and expectation. Yet after it was in position, it simply did not work. Because the primary mirror was misshapen, it was not until 1993 that the crew of the Shuttle Endeavor arrived like roadside mechanics, opened the hatch that was installed for the purpose, and replaced the defective mirror with a good one.
Suddenly, all that had originally been expected came true. The Hubble telescope was indeed the “window on the universe”, as it had originally been dubbed. When you look deep into space, you are actually looking back through time, because even though light travels at 186,000 miles a second, it requires time to get from one place to another. In fact, it is said that in some cases, the Hubble telescope is looking back eleven billion years to see galaxies already forming. The distant galaxies are speeding away from Earth, some travelling at the speed of light.
Hubble has viewed exploding stars such as the Eta Carinae, which clearly displayed clouds of gas and dust billowing outward from its poles at 1.5 million miles an hour. Prior to Hubble, it was visible from traditional telescopes on Earth, but its details were not as certainable. But now, the evidence of the explosion is obvious. The star still burns five million times brighter than the Sun and illuminates clouds from the inside.
Hubble has also provided a close look at black holes, which are described as comic drains. Gas and dust swirl around the drain and are slowly sucked in by the incredible gravity. It has also looked into an area that looked empty to the naked eye and, within a region the size of a grain of sand, located layer upon layer of galaxies, with each galaxy consisting of billions of stars.
The Hubble telescope was named after Edwin Hubble, a 1920s astronomer who developed a formula that expresses the proportional relationship of distances between clusters of galaxies and the speeds at which they travel. Astronomers use stars known as Cepheid variables to measure distances in space. These stars dim and brighten from time to time, and they are photographed over time and charted. All the discoveries made by Hubble have allowed astronomers to learn more about the formation of early galaxies.

The word “it” in paragraph 1 refers to ............

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After the Anasazi abandoned southwestern Colorado in the late 1200s or early 1300s, history’s pages are blank. The Anasazi were masons and apartment builders who occupied the deserts, river valleys, and mesas of this region for over a thousand years, building structures that have weathered the test of time.
The first Europeans to visit southwestern Colorado were the ever-restless, ambitious Spanish, who sought gold, pelts, and slaves. In 1765, under orders from the Spanish governor in Santa Fe, Juan Maria Antonio Rivera led a prospecting and trading party into the region. Near the Dolores River in southwestern Colorado, he found some insignificant silver-bearing rocks, and it is thought that it was he who named the mountains nearby the Sierra de la Plata or the Silver Mountains. Rivera found little of commercial value that would interest his superiors in Santa Fe, but he did open up a route that would soon lead to the establishment of the Old Spanish Trail. This expedition and others to follow left names on the land which are only reminders we have today that the Spanish once explored this region.
In 1776, one of the men who had accompanied Rivera, Andre Muniz, acted as a guide for another expedition. That party entered southwestern Colorado in search of a route west to California, traveling near today’s towns of Durango and Dolores. Along the way, they camped at the base of a large green mesa which today carries the name Mesa Verde. They were the first Europeans to record the discovery of an Anasazi archeological site in southwestern Colorado.
By the early 1800s, American mountain men and trappers were exploring the area in their quest for beaver pelts. Men like Peg-leg Smith were outfitted with supplies in the crossroads trapping town of Taos, New Mexico. These adventurous American trappers were a tough bunch. They, possibly more than any other newcomers, penetrated deeply into the mountain fastness of southwestern Colorado, bringing back valuable information about the area and discovering new routes through the mountains. One of the trappers, William Becknell, the father of the Santa Fe Trail, camped in the area of Mesa Verde, where he found pottery shards, stone houses, and other Anasazi remains.

The phrase “the region” in paragraph 2 refers to     .

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The pain of a migraine headache can virtually disable a person who suffers from it. Millions and millions of people suffer from migraines, although many of them do not even recognize that a migraine is different from a regular headache. A migraine is not at all the same as a normal headache, and it seems to have a very physical cause.
One symptom of a migraine is a precursor, which is a visual aura before an attack. Yet only about a third of patients actually experience that, and it is therefore not a requirement in the diagnosis. Other symptoms include increased pain when a person moves, nausea, and sensitivity to light and sound. Scientists now believe that migraines are caused, not by abnormal blood vessels as previously believed, but instead by a unique electrical disorder of brain cells. Physicians used to treat migraines with medicine to constrict blood vessels because of the belief that dilated blood vessels were the cause.
The new research has been enhanced by imaging devices that allow scientists to watch patients' brains during an attack. The results show that sufferers have abnormally excitable neurons, or brain nerve cells. Prior to the attack, the neurons suddenly fire off electrical pulses at the back of the brain, which ripple like waves on a lake after a stone hits the water. They ripple across the top and then the back of the brain, ultimately affecting the brain stem where the pain centers are located. The pain then generates possibly from the brain stem itself or from blood vessels inflamed by the rapidly changing blood flow, or perhaps from both.
Scientists have experimented by applying a powerful magnet to stimulate the neurons and discovered that some people's brains react differently than others'. When stimulation was applied to the brains of people who had suffered migraines, they saw the initial aura, and some actually suffered migraines. When the same stimulation was applied to the brains of people who had never suffered migraines, they realized no effect and the neurons showed no change.
Scientists and doctors continue to work on the research in an attempt to find the perfect treatment. It is considered important to treat migraines because it is believed that prolonged untreated attacks could cause physical changes in the brain leading to chronic pain.

According to the passage, now that scientists know that unusual neurons in certain people are the cause of migraines, they

Are organically grown foods the best food choices? The advantages claimed for such foods over conventionally grown and marketed food products are now being debated. Advocates of organic foods - a term whose meaning varies greatly - frequently proclaim that such products are safer and more nutritious than others.
The growing interest of consumers in the safety and nutritional quality of the typical North American diet is a welcome development. However, much of this interest has been sparked by sweeping claims that the food supply is unsafe or inadequate in meeting nutritional needs.
Although most of these claims are not supported by scientific evidence, the preponderance of written material advancing such claims makes it difficult for the general public to separate fact from fiction. As a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore.
Almost daily the public is besieged by claims for “no-aging” diets, new vitamins, and other wonder foods. There are numerous unsubstantiated reports that natural vitamins are superior to synthetic ones, that fertilized eggs are nutritionally superior to unfertilized eggs, that untreated grains are better than fumigated grains, and the like.
One thing that most organically grown food products seem to have in common is that they cost more than conventionally grown foods. But in many cases consumers are misled if they believe organic foods can maintain health and provide better nutritional quality than conventionally grown foods. So there is real cause for concern if consumers, particularly those with limited incomes, distrust the regular food supply and buy only expensive organic foods instead.

The “welcome development” mentioned in line 6 is an increase in ..........

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Thirty years ago, Lake Ponkapog in Hartwell, New Jersey, was full of life. Many birds and animals lived beside the water, which was full of fish. Now there are few birds, animals, and fish. The lake water is polluted. It is a dirty brown colour, and it is filled with strange plants.
How did this happen? First, we must think about how water gets into Lake Ponkapog. When it rains, water comes into the lake from all around. In the past, there were woods all around Lake Ponkapog, so  the rainwater was clean.
Now there are many homes on the lake hore. People often use the chemicals in their gardens. They use other chemicals inside their houses for cleaning and killing insects. There are also many businesses. Businesses use chemicals in their machines or stores. Other chemicals fall onto the ground from cars or trucks. When it rains, the rainwater flows by these homes and businesses. It picks up all the chemicals and then pours them into the lake. They pollute the water and kill the animal life.
There is still another problem at the lake: exotic plants. These plants come from other countries. They have no natural enemies here, and they grow very quickly. In a short time, they can fill up a lake. Then there is no room for other plants. The plants that normally grow there die. These plants gave many animals and fish their foods or their homes. So now those animals and fish die, too.
People in Hartwell are worried. They love their lake and want to save it. Will it be possible? A clean lake must have clean rainwater going into it. Clean rainwater is possible only if people are more careful about chemicals at home and at work. They must also be more careful about gas and oil and other chemicals on the ground.

Chemicals from homes and businesses     .

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   Before the mid-nineteenth century, people in the United States ate most foods only in season. Drying, smoking and salting could preserve meat for a short time, but the availability of fresh meat, like that of fresh milk, was very limited; there was no way to prevent spoilage. But in 1810, a French inventor named Nicolas Appert developed the cooking-and-sealing process of canning. And in the 1850’s an American named Gail Borden developed a means of condensing and preserving milk. Canned goods and condensed milk became more common during the 1860’s, but supplies remained low because cans had to be made by hand. By 1880, however, inventors had fashioned stamping and soldering machines that massproduced cans from tinplate. Suddenly all kinds of food could be preserved and bought at all times of the year.

   Other trends and inventions had also helped make it possible for Americans to vary their daily diets. Growing urban population created demand that encouraged fruit and vegetable farmers to raise more produce. Railroad refrigerator cars enabled growers and meat packers to ship perishables great distances and to preserve them for longer periods. Thus, by the 1890’s, northern city dwellers could enjoy southern and western strawberries, grapes, and tomatoes, previously available for a month at most, for up to six months of the year. In addition, increased use of iceboxes enabled families to store perishables. As easy means of producing ice commercially had been invented in the 1870’s, and by 1900 the nation had more than two thousand commercial ice plants, most of which made home deliveries. The icebox became afixture in most homes and remained so until the mechanized refrigerator replaced it in the 1920’s and 1930’s.

   Almost everyone now had a more diversified diet. Some people continued to eat mainly foods that were heavily in starches or carbohydrates, and not everyone could afford meat. Nevertheless, many families could take advantage of previously unavailable fruits, vegetables, and dairy products to achieve more varied fare.

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On the tiny island of Flores, east of Bali and midway between Asia and Australia, the scientists have discovered the remains of a small, hobbit-like species of humans. These people grew no larger than the modern three-year-old child. They lived about 18,000 years ago and are completely different species of human.
This discovery has taught scientists a lot about the human species. This remarkable discovery shows that the human species is more varied and flexible in its ability to adapt than previously thought. These hobbit-like people join a short list of other type of humans that lived with modern humans.
The researchers believe that these hobbits evolved from a normal size, human population that reached Flores around 840,000 years ago. One likely explanation is that, over thousands of years, the species became smaller because the environmental conditions favored a smaller body size. The dwarfing of mammals on islands occurs frequently. Islands limit food supply and predators and species compete for the same environmental space. Survival would depend on minimizing energy requirements.

The word “remains” in the passage is closest in meaning to     .