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marsa1989

3.    (24275-!-item-!-188;#058&000768)

 

The prairie vole, a small North American grassland rodent, breeds year-round, and a group of voles living together consists primarily of an extended family, often including two or more litters.  Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups.  The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.

 

Which of the following, if true, provides the strongest support for the explanation offered?

(A) It is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.

(B) Prairie vole populations vary dramatically in size from year to year.

(C) The prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.

(D) Winters in the prairie voles' habitat are often harsh, with temperatures that drop well below freezing.

(E) Snakes, a major predator of young prairie voles, are active only from spring through early autumn.

我上网看了一下，的确是春夏秋的时候蛇出没，导致老鼠每巢的死亡率很高，可我当时误以为团结就是力量了。。。怎么觉得困难的时候才应该在一起。。。Ｄ为什么不对？冬天条件差，所以要在一起，是因为没提到老鼠么？ 谢谢牛牛们！！！！

easttiger

关键是D是irrelevant.

因为问题点名道姓指the explanation,也就是the explanation of为什么鼠群的大小按照之前提到的方式随季节而变--这是因为幼鼠的死亡率会随季节而变动。

D的解释和幼鼠死亡率随季节变动没有一点关系。

stavan

楼主解题应该紧扣文章信息, 不要擅自引申....

文章中什么时候说过团结就是力量? 什么时候说条件恶劣就一定要在聚在一起? 如果条件恶劣,缺少食物, 更应该分散开去寻找食物怎么办?

同时...看了楼主自己的分析, 发现楼主并没有理解题目的意思, group size的大小, 不是说是分散开还是聚在一起导致的

文章说是因为死亡率的关系, 问题问加强, 即使是因为条件恶劣就真的需要聚在一起, 那也是削弱结论

而且是标准的他因削弱....

如果楼主还有时间, 我建议在好好过一遍og..重新理一下解题思路...

marsa1989

还是有点不明白。。。为什么是死亡率低的时候聚在一起？D那样因为死亡率高所以聚在一起不可以么？脑子转不过来了，谢谢

ruud

选E,D没有support啊，冬天条件恶劣所以鼠群规模下降啊，出题人的意思不是什么聚在一起不聚在一起，是条件好群体规模就大，幼鼠死的少，反之亦然

[此贴子已经被作者于2008-8-5 21:53:00编辑过]