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.
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 adapted. 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, even affect 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. The 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 revolutionary history may reflect a sequence of essentially random events.
Why is “plankton” mentioned?
A. To illustrate a comparison between organisms that live on the land and those that live in the ocean
B. To point out that certain species could never become extinct.
C. To emphasize the importance of food resources in preventing mass extinction.
D. To demonstrate the interdependence of different species
Đáp án : D
Đặt từ này trong ngữ cảnh đoạn văn: 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 => sự hủy diệt quy mô lớn có thể xảy ra do sự thay đổi khá nhanh trong môi trường và có thể xấu hơn nữa bởi mối quan hệ tương tác giữa các loài. Sau đó đoạn văn đưa ra ví dụ (for example) về loài sinh vật phù du (plankton) biến mất có thể làm giảm lượng ô-xi, ảnh hưởng đến sinh vật khác -----> Plankton được đưa ra để minh họa về mối quan hệ tương tác giữa các loài