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 strengthens the argument?

1. 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.

2. 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.

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

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

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

答案是A，请问怎么推出来的？原文能看懂。

A的意思是研究开始时的参与者中depressed的和not depressed的在研究结束时变成吸烟者的可能性是一样的.

选项A排除了这样一种会削弱原文结论的可能: 即某些本来就是depressed在该研究的过程中变成了吸烟者.这样就削弱了吸烟造成depress的结论

同意楼上的观点。

这道题目也曾经困扰我很久。后来是一位逻辑大牛告诉我的：ets很喜欢考这类逻辑题。“B的发生不能导

致A的发生”能够加强“A的发生导致B的发生"的结论。

大家觉得有道理吗？

基本同意，我是这么理解的：B不能导致A，排除了因果倒置的削弱，所以加强了A导致B。

大家觉得对吗？

个人觉的这个A就是文章的assumption，A取费削弱，如果不取非就是一种加强，将assumption列出来。记得FeiFei有把assumption题按做加强的做法去做。这题刚好反一下，把assumption作为加强题的答案。