In the late 1980's, the population of sea otters in the North Pacific Ocean began to decline. Of the two plausible explaination for the decline-increased predation by killer whales or diease-diease is more likely. After all, a concurrent sharp decline in the populations of seals and sea lions was almost certainly caused by a pollution-related diease, which could could have spead to sea otters, whhereas the population of killer whales did not change noticeably.

Which of the following, if true, would most seriously weaks the reasoning?

A. Killer whales in the North Pacific usually prey on seals and sea lions but will, 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 North Pacific in the 1980's

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

D,Following the decline 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

哪位好心人士，帮忙解答下，我搞了半天，都要晕了。。

 选A

题设由sharp decline of seals and sea lions （almost caused by a pollution-related diease）→decline of sea otters was also by the same reason

得出两个plausible的explaination  其中一个更likely

想要weaken

就要找出一个对另一个explaination 有利 往那个方向发展的选项

而且最好要用到已知的seals and sea lions 的条件

A很好的实现了

说seals and sea lions由于污染数量减少了 whales要另寻猎物了 不就很可能成为otters减少的原因了吗

有利于我们得出第一个explaination更likely

weaken

哈哈 嗯嗯 我懂了 哎 没掌握方法呀~~  当时只想到到怎样把"disease"那个寻找他因来weaken，根本没

想到只要通过加强另一个就可以解决问题了。 哎~~这么个问题我都解决不了，20号要考了 好担心呀 ~~~ 我的逻辑练了很久还是上不去， 谢谢！！