一道GWD！！

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A。这道题很典型，就是讨论两个现象伴随发生究竟谁是因谁是果的问题。原题说，在从未吸烟的一组青少年中，在实验过程中更早开始吸烟的那些人更容易抑郁。结论说是吸烟中摄取的N使人抑郁。问加强选项。原文说吸烟导致抑郁。A选项是说，那些从一开始就更容易抑郁的人不会更有可能吸烟。A就是说，不是抑郁导致吸烟。这样可以起到加强的效果。A取反后又削弱的效果，本身就有加强的效果。

抑郁不会导致吸烟就能加强吸烟导致了抑郁，好像也有点道理，我昨天也在纠结这个问题