2021年托福阅读PASSAGE 77 试题及答案

2021年托福阅读PASSAGE 77

试题及答案

PASSAGE 77

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.

1. The word "it" in line 3 refers to

(A) environment

(B) species

(C) extinction

(D) 99 percent

2. The word "ultimately" in line 8 is closest in meaning to

(A) exceptionally

(B) dramatically

(C) eventually

(D) unfortunately

3. What does the author say in paragraph 1 regarding most species in Earth's

history

(A) They have remained basically unchanged from their original forms.

(B) They have been able to adapt to ecological changes.

(C) They have caused rapid change in the environment.

(D) They are no longer in existence.

4. Which of the following is NOT mentioned in paragraph 1 as resulting from

rapid ecological change?

(A) Temperature changes

(B) Availability of food resources

(C) Introduction of new species

(D) Competition among species

5. The word "demise" in line 12 is closest in meaning to

(A) change

(B) recovery

(C) help

(D) death

6. Why is "plankton" mentioned in line 17?

(A) To demonstrate the interdependence of different species.

(B) To emphasize the importance of food resources in preventing mass extinction.

(C) To illustrate a comparison between organisms that live on the land and those

that live in the ocean.

(D) To point out that certain species could never become extinct.

7. According to paragraph 2, evidence from fossils suggests that

(A) Extinction of species has occurred from time to time throughout Earth's history.

(B) Extinctions on Earth have generally been massive

(C) There has been only one mass extinction in Earth's history.

(D) Dinosaurs became extinct much earlier than scientists originally believed.

8. The word "finding" in line 20 is closest in meaning to

(A) published information

(B) research method

(C) ongoing experiment

(D) scientific discovery

9. Which of the following can be inferred about the theory mentioned in Line

21-23?

(A) Many scientists could be expected to disagree with it.

(B) Evidence to support the theory has recently been found.

(C) The theory is no longer seriously considered.

(D) Most scientists believe the theory to be accurate.

10. In paragraph 3, the author makes which of the following statements about

a species' survival?

(A) It reflects the interrelationship of many species.

(B) It may depend on chance events.

(C) It does not vary greatly from species to species

(D) It is associated with astronomical conditions.

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

species occurred

(A) 26 million years ago

(B) 65 million years ago

(C) 225 million years ago

(D) 250 million years ago

ANSWER KEYS

PASSAGE 77 BCDCD AADAB C