求教一道逻辑题

nk776

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?

• AIt is in the spring and early summer that prairie vole communities generally contain the highest proportion of young voles.
• BPrairie vole populations vary dramatically in size from year to year.
• CThe prairie vole subsists primarily on broad-leaved plants that are abundant only in spring.
• DWinters in the prairie voles' habitat are often harsh, with temperatures that drop well below freezing.
• ESnakes, a major predator of young prairie voles, are active only from spring through early autumn.
  

我的答案：A

正确答案：E

我的理解是 a选项加强了Pv community 的确有高比例的young voles。而题干的claim说到原因是mortality of young 。a选项不是更能说明是Young的问题吗？因为高比例的Young 死了的确community会变得更小了。求各位大神解答，不胜感谢！！

spicytaco

背景：Voles commonly live in large groups from late autumn through winter; from spring through early autumn, however, most voles live in far smaller groups  深秋及冬的group大于春至初秋的group

结论：The seasonal variation in group size can probably be explained by a seasonal variation in mortality among young voles.      季节性的幼年Voles死亡率可以用来解释 季节性的group size变化

问加强...或者换个问法，下面那个选项可以合理解释结论

A 一般在春天,初夏的时候 young voles数量最高

这放在上面不是和     深秋及冬的group大于春至初秋的group    矛盾了么？ 背景说是春夏的group size要小啊

E天敌蛇只在春天至初秋活动     这就合理解释了为什么同时期group size会小，而之后group size会大些 （living together consists primarily of an extended family, often including two or more litters）

nk776

spicytaco 发表于 2018-11-17 09:45
背景：Voles commonly live in large groups from late autumn through winter; from spring through early ...

同意！               

雷东宝

spicytaco 发表于 2018-11-17 09:45
背景：Voles commonly live in large groups from late autumn through winter; from spring through early ...

这个解释不对。
A选项说的是“春夏V群落的年轻个体比重，比秋冬的V群落年轻个体比重大”
按照题干的结论来说（可以用年轻个体的死亡率来解释V群落数量的季节性变化），似乎是和A相符的。

但仔细看，A并不能支持conclusion。因为即使不同季节，年轻个体的比重不同，群落V的总数变化也有可能是因为其他年龄段个体（如成年个体）的变化而造成的。比如young V的比重像A说的，在春夏比较多，但倘若他们从春夏到秋冬都没死，这期间死的都是成年个体，那A就不能support这个结论了。

所以，A不必然支持结论

你尝

A.group size是total number,而proportion是相对占比 两者间irrelevant