Câu hỏi:
24/03/2020 2,366Read 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 from 28 to 34.
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 became 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 approximately 95 percent of all species died, mass extinctions 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 oceans. 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 or inability to adapt. If so, some of evolutionary history may reflect a sequence of essentially random events.
The word “it” in paragraph 1 refers to _________
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CÂU HỎI HOT CÙNG CHỦ ĐỀ
Câu 1:
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Not only _________ the exam but she also got a scholarship.
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24/03/2020
34,786
Câu 2:
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that best completes each of the following exchanges.
Tom: “How did you get here?” - John: “ _________”
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24/03/2020
22,362
Câu 3:
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.
"If I were you, I’d buy that house." Ms. Hoa said to Ms. Lan.
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15/03/2020
14,183
Câu 4:
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
Rarely have I visited _________ Bangkok, the capital of Thailand.
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24/03/2020
13,210
Câu 5:
Mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.
His _________ and bad work led to his dismissal from the company.
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15/03/2020
13,156
Câu 6:
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.
His dog was so fierce that nobody would visit him.
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15/03/2020
12,340
Câu 7:
Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to each of the following questions.
You needn’t hurry because there is a delay of about two hours.
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15/03/2020
12,115
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