【求助】prep 07 cr1 22题~~！！谢谢各位！感激不尽！！！！

gege112

22.    (28829-!-item-!-188;#058&003748)

In the late 1980s, the population of sea otters in the North Pacific began to decline.  There are two plausible explanations for the decline:  predation, possibly by killer whales, or disease.  Of these two, disease is the more likely, since a concurrent sharp decline in populations of seals and sea lions is believed to have been caused by disease, and diseases that infect these creatures are likely to be able to infect sea otters also.

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 will, when this food source is scarce, seek out other prey.
(B) There is no indication that the sea otter population at any North Pacific location declined in the 1980s because of substantial numbers of sea otters migrating to other locations.
(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 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.

A选项为正确答案，但是，kill whale没有seals 和sea lion吃了，并没有说一定会去吃sea otters啊 ？这算是我们主观加的条件吗？

wbw414

我觉得在这个题干中用的是类比法，作者说因为seals and sea lions的下降是由disease引起的，从而推断sea otter的下降也是由于disease引起的。但是如果seal and sea lions的下降不是由于disease引起的呢，而是由于whales引起的，是A选项里说的，那么，我们同样用类比的方法推断，sea otter的下降是由于whale引起的，从而削弱了结论。

DriveChange

先看题，是weaken类型，所以先找结论，再看前提。
结论1：Seal和lion decline；前提：disease (而且是believed，也就是事实）
结论2：Otter decline；可能前提：（a）被whale kill（b）disease

看答案：
（A）Seal和lion下降-->whale没有吃的了-->吃Otter，所以证明了可能前题（a）
（B）由于移居-->Otter少了（no indication）；跟原文中可能前提无关，排除
（C）1980年Otter与之前时代比少了；与1980年代内otter为什么decline无关；排除
（D）Otter decline --->另一物种增多了；没有说明为什么otter decline，只是另一个递进的因果；排除
（E）seal和lion比otter分布广，不是前提，与otter decline无关；排除

christina5091

我想问C选项为什么不算是给出他因

gege112

谢谢一楼和二楼的大大·~~明白了不少！！~~~~~

DriveChange

一个说的是1980s之外的事情，一个说的是1980s之内的事。何来他因呢