Researchers took a group of teenagers who had never smoked and for one year tracked whether they took up smoking and how their mental health changed. Those who began smoking within a month of the study’s start were four times as likely to be depressed at the study’s end than those who did not begin smoking. Since nicotine in cigarettes changes brain chemistry, perhaps thereby affecting mood, it is likely that smoking contributes to depression in teenagers.

Which of the following, if true, most strengthen the argument?

A. Participants who were depressed at the study’s start were no more likely to be smokers at the study’s end than those who were not depressed.

B. Participants who began smoking within a month of the study’s start were no more likely than those who began midway through to have quit smoking by the study’s end.

C. Few, if any, of the participants in the study were friends or relatives of other participan

D. Some participants entered and emerged from a period of depression within the year of the study.

E. The researchers did not track use of alcohol by the teenagers.

Why A is correct?

排除他因.

结论说吸烟让人沮丧. 加强的A说，沮丧的人不比不沮丧的人更容易吸烟,也就是说，大家吸烟的机会是平等的,在平等的情况下，可以推出吸烟让人沮丧.如果沮丧的人更愿意吸烟,那他们做比较的前提就不相等了.

今天错这个题突然有一种感觉，好像经常有类似的题目。它们的它因貌似非常远。

做这题的时候看到A 脑子就开始短路了。

用POE 排除了其他的选项 就选了A

A选项相当于是排除实验的可能误差－－即使试验的起点相同。如果起点不相同，那么试验结论就没有说服力。所以，A支持。GMAT中有很多这样的加强题。大家遇到比较或者对比试验的加强题，可以朝这个方面预测答案。

我觉得 结论说 吸烟导致沮丧

       A说    沮丧不导致吸烟

很像排除因果倒置

好似很多类似的题

不知道这么想对不对 待指点

明白啊。

其实主要是AB两个选项读起来不太好懂，所以才有问题……