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OG20官方指南,建议同学们刷3遍。第一遍做题了解题型和考点,第二遍精刷,第三遍集中解决疑难问题。建议考生第一遍刷题采用官方正版纸质书籍,若遇到疑难问题,欢迎在此专区查阅解析,提供解析,参与题目讨论,与所有考生一起解决疑难问题。
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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 researchers 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, longterm data will not soon be forthcoming, and postponing environmental action while we wait for it may doom species and whole ecosystems to extinction.

【OG20-P447-573题】

According to the passage, each of the following is true of endangered amphibian species EXCEPT:

  • 分析A选项
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  • 分析B选项
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  • 分析C选项
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  • 分析D选项
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  • 分析E选项
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当前版本由 感觉自己萌萌哒 更新于2015-11-03 11:06:02 感谢由 感觉自己萌萌哒 对此题目的解答所做出的贡献。
细节题
定位第2段:An endangered population is always rare(对应A), almost always small(对应B), and, by definition, under constant threat of extinction (对应C)even without a proximate cause in human activities(对应E). 选D
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.
原文相反,第二段最后一句: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
E They are in danger of extinction due to events that sometimes have nothing to do with human activities.

题目讨论 2条评论)

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    286053m

    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.
    定位到这句话了,说许多1950年代的A在下降后恢复了,所以现在处在下降危机中的A也许也会recover。
    和 C相反,故选C.
    1 0 回复 2020-08-16 11:38:05
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    见过夏天去非洲拍动物世界

    题干说true of endangered amphibian species,已经将范围限制到endangered。
    文章区分了两种不同的情境,主要是为了解释将一种现象简单归结到其中一种情境的不合理之处。
    但是既然题干已经将这种现象中的物种归结到一种情境中,那么就应该按照这种情境中的特征来回答问题。
    谨记。
    0 0 回复 2016-12-30 13:41:32
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