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本题由chris提供
2443 次学习

In the late 1980s, the population of sea otters in

the North Pacific Ocean began to decline. Of the two plausible explanations for the decline— increased predation by killer whales or disease—disease is the more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related disease, which could have spread to sea otters, whereas the population of killer whales did not change noticeably.


Which of the following, if true, most seriously weakens the reasoning?



    A. Killer whales in the North Pacific usually prey on seals and sea lions but wil, when this food source is scarce, seek out other prey.

    B. There is no indication that substantial numbers of sea otters migrated to other locations from the North Pacific in the 1980s.

    C. Along the Pacific coast of North America in the 1980s, sea otters were absent from many locations where they had been relatively common in former times.

    D. Following the in the population of the sea otters, there was an increase in the population of sea urchins, which are sea otters’ main food source.

    E. The North Pacific populations of seals and sea lions cover a wider geographic area than does the population of sea otters.


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答案:
A
在1980年代
期,北太平洋的海狸的数量开始下降。两个可能的解释是:杀手鲸的捕食,或者疾病。 在这两者中,疾病更可能,由于海豹和海狮的大量下降的原因是疾病,传染这些动物的疾病也可能感染海狸。 削弱题 可用类比思维 A 杀手鲸一般都会捕食海豹和海狮,但是当食物少的时候,也会捕食其他动物;捕食其他动物就是指海狸,说明海狸可能是因为杀手鲸的捕猎导致数量下降,而非疾病,削弱结论,正确 B 没有迹象表明因为大量海狸迁移到其他地点,导致海狸在1980年代北太平洋的海狸数量下降;无关,排 C 1980年代沿着北美太平洋沿岸,海狸在原来相对普遍的地方也看不到了; 没谈下降原因,无关,排 D 在海狸数量下降后,海胆的数量上升了,海胆是海狸的主要食物来源; 跳出范围,排 E 北太平洋海豹和海狮的活动范围比海狸的活动范围大; 无关比较,排

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