It is estimated that over 99 percent of all species that ever existed have become extinct. What causes extinction? When a species is no longer adapted to a changed environment, it may perish. The exact causes of a species’ death vary from situation to situation. Rapid ecological change may render an environment hostile to a species. For example, temperatures may change and a species may not be able to adapt. Food resources may be affected by environmental changes, which will then cause problems for a species requiring these resources. Other species may become better adapted to an environment, resulting in competition and, ultimately, in the death of a species.

The fossil record reveals that extinction has occurred throughout the history of Earth. Recent analyses have also revealed that on some occasions many species become extinct at the same time- a mass extinction. One of the best- known examples of mass extinction occurred 65 million years ago with the demise of dinosaurs and many other forms of life. Perhaps the largest mass extinction was the one that occurred 225 million years ago, when appropriately 95 percent of all species died. Mass extinction can be caused by a relatively rapid change in the environment and can be worsened by the close interrelationship of many species. If, for example, something were to happen to destroy much of the plankton in the oceans, then the oxygen content of Earth would drop, affection even organisms not living in the ocean. Such a change would probably lead to a mass extinction. One interesting, and controversial, finding is that extinctions during the past 250 million years have tended to be more intense every 26 million years. This periodic extinction might be due to intersection of the Earth’s orbit with a cloud of comets, but this theory is purely speculative. Some researchers have also speculated that extinction may often be random. That is, certain species may be eliminated and others may survive for no particular reason. A species’ survival may have nothing to do with its ability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.

According to the passage, it is believed that the largest extinction of a species occurred ...........

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• The author’s main purpose is to...

• Which of the following would the writer support?

• The word “they” in bold in paragraph 2 refers to ...............

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• What does the word “depletion” in paragraph 2 probably mean?

• What can be inferred about the defense mechanisms of the sea cucumber?

• The author claims all of the following to be the benefits of rooftop gardens except .............

• The word “classic” in paragraph 3 is closest in meaning to ............

• The writer learnt to sail .................

• The word “bounds” in line 5 is closest in meaning to ........

• Sign language is said to be very picturesque and exact and can be used internationally EXCEPT for ..........

• Which of the following best describes the organization of the passage?

• How did children feel when viewing a special series of 15-minute program at school?

• The following statements are correct EXCEPT that ........

• The word it in the first paragraph refers to ___.

• Why were the telephone, radio, and television invented?

• The word “sensational” is closest in meaning to .............

• When was M.L. born?

• According to paragraph 1, which of the following is NOT true?

• Approximately when did English begin to be used beyond England?

• What does the author imply in the last sentence of the passage?