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There are recent reports of apparently drastic declines in amphibian populations and of extinctions of a number of the world's endangered amphibian species. These declines, if real, may be signs of a general trend toward extinction, and many environmentalists have claimed that immediate environmental action is necessary to remedy this "amphibian crisis", which, in their view, is an indicator of general and catastrophic environmental degradation due to human activity.
To evaluate these claims, it is useful to make a preliminary distinction that is far too often ignored. A declining population should not be confused with an endangered one. An endangered population is always rare, almost always small, and, by definition, under constant threat of extinction even without a proximate cause in human activities. Its disappearance, however unfortunate, should come as no great surprise. Moreover, chance events—which may indicate nothing about the direction of trends in population size—may lead to its extinction. The probability of extinction due to such random factors depends on the population size and is independent of the prevailing direction of change in that size.
For biologists, population declines are potentially more worrisome than extinctions. Persistent declines, especially in large populations, indicate a changed ecological context. Even here, distinctions must again be made among declines that are only apparent (in the sense that they are part of habitual cycles or of normal fluctuations), declines that take a population to some lower but still acceptable level, and those that threaten extinction (e.g., by taking the number of individuals below the minimum viable population). Anecdotal reports of population decreases cannot distinguish among these possibilities, and some amphibian populations have shown strong fluctuations in the past.
It is Indisputably true that there is simply not enough long-term scientific data on amphibian populations to enable researches to identify real declines in amphibian populations. Many fairly common amphibian species declared all but extinct after severe declines in the 1950s and 1960s have subsequently recovered, and so might the apparently declining populations that have generated the current appearance of an amphibian crisis. Unfortunately, long-term data will not soon be forthcoming, and postponing environmental action while we wait for it may doom species and whole ecosystems to extinction.
1. The primary purpose of the passage is to
(A) assess the validity of a certain view
(B) distinguish between two phenomena
(C) identify the causes of a problem
(D) describe a disturbing trend
(E) allay concern about a particular phenomenon
2. It can be inferred from the passage that the author believes which of the following to be true of the environmentalists mentioned in lines 5-6?
(A) They have wrongly chosen to focus on anecdotal reports rather than on the long-term data that are currently available concerning amphibians.
(B) Their recommendations are flawed because their research focuses too narrowly on a single category of animal species.
(C) Their certainty that population declines in general are caused by environmental degradation is not warranted.
(D) They have drawn premature conclusions concerning a crisis in amphibian populations from recent reports of declines.
(E) They have overestimated the effects of chance events on trends in amphibian populations.
3. It can be inferred from the passage that the author believes which of the following to be true of the amphibian extinctions that have recently been reported?
(A) They have resulted primarily from human activities causing environmental degradation.
(B)They could probably have been prevented if timely action had been taken to protect the habitats of amphibian species.
(C) They should not come as a surprise, because amphibian populations generally have been declining for a number of years.
(D) They have probably been caused by a combination of chance events.
(E) They do not clearly constitute evidence of general environmental degradation.
4. According to the passage, each of the following is true of endangered amphibian species EXCEPT:
(A) They are among the rarest kinds of amphibians.
(B) They generally have populations that are small in size.
(C) They are in constant danger of extinction.
(D) Those with decreasing populations are the most likely candidates for immediate extinction.
(E) The are in danger of extinction due to events that sometimes have nothing to do with human activities.
5. Which of the following most accurately describes the organization of the passage?
(A) A question is raised, a distinction regarding it is made, and the question is answered.
(B) An interpretation is presented, its soundness is examined, and a warning is given.
(C) A situation is described, its consequences are analyzed, and a prediction is made.
(D) Two interpretations of a phenomenon are described, and one of them is rejected as invalid.
(E) Two methods for analyzing a phenomenon are compared, and further study of the phenomenon is recommended.
6. Which of the following best describes the function of the sentence in lines 35-38 [Anecdotal reports of population decreases cannot distinguish among these possibilities, and some amphibian populations have shown strong fluctuations in the past.]?
(A) To give an example of a particular kind of study
(B) To cast doubt on an assertion made in the previous sentence
(C) To raise an objection to a view presented in the first paragraph
(D) To provide support for a view presented in the first paragraph
(E) To introduce an idea that will be countered in the following paragraph
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发表于 2021-4-19 15:26:58
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