Humans have struggled against weeds since the beginnings of agriculture. Marring our gardens is one of the milder effects of weeds - any plants that thrive where they are unwanted. They clog waterways, destroy wildlife habitats, and impede farming. Their spread eliminates grazing areas and accounts for one-third of all crop loss. They compete for sunlight, nutrients, and water with useful plants.

   The global need for weed control had been answered mainly by the chemical industry. Its herbicides are effective and sometimes necessary, but some pose serious problems, particularly if misused.

   Toxic compounds threaten animal and public health when they accumulate in food plants, groundwater, and drinking water. They also harm workers who apply them.

   In recent years, the chemical industry has introduced several herbicides that are more ecologically sound. Yet new chemicals alone cannot solve the world's weed problems. Hence, scientists are exploring the innate weed-killing powers of living organisms, primarily insects and microorganisms. The biological agents now in use are environmentally benign and are harmless to humans. They can be chosen for their ability to attack selected targets and leave crops and other plants untouched. In contrast, some of the most effective chemicals kill virtually all the plants they come in contact with, sparing only those that are naturally resistant or have been genetically modified for resistance. Furthermore, a number of biological agents can be administered only once, after which no added applications are needed. Chemicals typically must be used several times per growing season.

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions

With what topic does this passage primarily deal?

Câu hỏi liên quan

• According to the passage, what is implied about tea harvesting?

• How many different forms of communication are mentioned here?

• Which of the following threatens the countryside in Britain?

ZUNIA12

• Animals found desert living possible only _____

• According to the article, what does the band Four Square hope to do in the future?

• Which of the following is NOT true, according to the passage?

• What can the word adorning be best replaced by?

• A patient can still live a comfortable life even after the removal of ..........

• The word “indiscriminately” could best be replaced by which of the following?

• According to the passage, an overconfident front may hide _______.

• The reason why telecommuting has not become popular is that the employees .............

• What does the word "run" in the last paragraph mean?

• According to the passage, which of the following countries attracts more tourists than the others?

• In the passage, the author’s attitude towards “mixed-ability teaching” is_____.

• What is the main idea of the passage?

• The word “reluctant” in the third paragraph can best be replaced by ............

• The word “them” in the second paragraph refers to ................

• According to paragraph 3, which of the following fields is NOT suitable for a person who does not want to live in a big city?

• The passage mentions which of the following as a reason for the importance of Lake Vostok to scientists?

• All of the following statements are true EXCEPT______________