19. Identical twins tend to have similar personalities; if environment outweighs heredity in personality development, twins raised together should presumably have more similar personalities than those raised apart. A recent study of identical twins in both situations measured 11 key traits through a questionnaire, and concluded that 7 of the 11 are primarily products of heredity.

Which of the following, if established, would cast the most doubt on the study’s results?

(A) Fewer than half of the pairs of twins studied were raised separately. ?

(B) The ages of all of the twins studied fell within a 10-year range.

(C) Some of the traits that the study attributed to heredity developed in the separately raised twins because those pairs all grew up in similar families.

(D) Although over half the traits measured were determined to be linked to heredity, the nature of those traits varied widely. （C）

(E) The 11 traits that were measured constitute a representative sample of larger, generally accepted pool of key personality traits.

正确答案是Ｃ．为什么Ａ不对啊？请教ＮＮ？

我这题也错了，但是后来发觉是自己理解太差：A recent study of identical twins in both situations measured 11 key traits through a questionnaire，这句话里的both situations表示有两批双胞胎，一批一起养大，还有一批分开养大，但是最后结果发现他们共同的特质与遗传有关。

所以反对的答案就是：那批分开养大的双胞胎其实在差不多的家庭里生长（即环境类似）

而A好像针对了条件，属于无关选项。

你是说A反对前提么？那么我想你错了！文中只有讲in both situations，但是没有讲是一半分开养一半一起养。

A之所以错是因为A完全就是不必要的条件。不管又多少分开养有多少不分开养其实都不影响研究的可信度。假设有1000个人参加调查，其中900个是在一起养的（叫做组X），100个是分开养的（组Y），而我们想要确定特点A是不是遗传的仍然没有问题。我们只需要确定在组X中的双胞胎同时存在或者不存在特点A的概率以及组Y中的双胞胎同时存在或者不存在特点A的概率，然后再做比较就可以得出是否与遗传有关了。如果两个概率一样就是遗传，如果不同就是后天的。

终于明白了.谢谢!

看来，我也是没有明白选项的意思.

原先觉得由于组Y的样本量小，可能导致结果有偏差，其实是我多虑了。因为比较的是概率.而且CR题目通常不会深究这种细节。