逻辑问题看进来

DendisUID: 158017

这是一篇gre国内95.04的阅读全真题，本来不该发在作文版，但其中探讨的问题似乎更多涉及逻辑，涉及assumption、conclusion问题，和argument有颇多联系，所以我就发到这里来了，也请各位逻辑强人帮助我解答困惑

One explanation for the tendency of animals to be more vigilant in smaller groups than in larger ones assumes that the vigilant behavior—looking up, for example—is aimed at predators. If individuals on the edge of a group are more vigilant because they are at greater risk of being captured, then individuals on average would have to be more vigilant in smaller groups, because the animals on the periphery of a group form a greater proportion of the whole group as the size of the group diminishes.
However, a different explanation is necessary in cases where the vigilant behavior is not directed at predators. J. Krebs has discovered that great blue herons look up more often when in smaller flocks than when in larger ones, solely as a consequence of poor feeding conditions. Krebs hypothesizes that the herons in smaller flocks are watching for herons that they might follow to better feeding pools, which usually attract larger numbers of the birds.
18.        Which of the following best describes the relationship of the second paragraph to the first?
(A) The second paragraph relies on different evidence in drawing a conclusion similar to that expressed in the first paragraph.
(B) The second paragraph provides further elaboration on why an assertion made at the end of the first paragraph proves to be true in most cases.
(C) The second paragraph provides additional information in support of a hypothesis stated in the first paragraph.
(D) The second paragraph provides an example of a case in which the assumption described in the first paragraph is unwarranted.
(E) The second paragraph describes a phenomenon that has the same cause as the phenomenon described in the first paragraph.
正确选项是D

可能复习argument的后遗症，也许是长期没有逻辑训练，第一次做这道题就开始搞概念。想弄清一段究竟什么conclusion，什么assumption。想着想着就有点晕～～～似乎走进自己设置的逻辑泥潭

从文章assumes that the vigilant behavior—looking up, for example—is aimed at predators.来看，assumption就是vigilant behavior is aimed at predators，那么结论又是什么呢？

我自己列了个三段论：因为警觉行为是针对掠食者并防止它们的攻击，而小群体中动物比大群体中动物更容易受到攻击，所以小群体中动物更警觉。

怪了，怎么结论变成“小群体中动物比大群体中动物更警觉”？如果是这样的话，那么两段的结论都是一样的，只是解释的内容不同，如此也就是说A选项也正确。

理性告诉我原本第一段的结论应该是：“因为警觉行为是针对掠食者的，所以小群体中动物更警觉。”它的结论本身就是一个复合句，但是这个结论的assumption究竟又是什么？vigilant behavior is aimed at predators作为assumption的话，如何推理得到这个复合结论？就在这里我反复痛苦思考，还是没想明白，请求大家帮助

poohUID: 146994

我的理解是，作者在试图解释vigilant behavior ，针对到底是什么引起了vigilant behavior做出了两种解释：
1是因为it is aimed at predators, 然后举例证明。用的是小群体中动物更警觉这个例子。注意，这仅是个例子，用来支持结论的。结论是vigilant behavior是aimed at predators的。
第二段又作了另一种解释。认为vigilant behavior是寻找食物的需要。因为小群体中的heron更多的抬头 in order to  follow to better feeding pools. 所以否定了第一段的结论。


therefore, D

DendisUID: 158017

有点不同意pooh的说法，不过还是多谢pooh，又见到你好开心啊！

我理解文章的主要内容是说explanation for the tendency of animals to be more vigilant in smaller groups than in larger ones 。这个从两段的首句分别得到验证。不同的是一段论证assume vigilant behavior is aimed at predators而二段则没有这样一个assumption。

这样，一段的结论是：因为警觉行为是针对掠食者的，所以小群体中动物更警觉。
二段的结论是：认为vigilant behavior是寻找食物的需要，所以小群体中动物更警觉。
它们所期待达成的论证结果都是说明animals to be more vigilant in smaller groups than in larger ones

所以我在这两个所谓的conclusion上——“因为警觉行为是针对掠食者的，所以小群体中动物更警觉”和“animals to be more vigilant in smaller groups than in larger ones ”就又混了起来，到底哪个才是1段的结论呢？那么它的assumption是什么呢？