Q16:

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.

 A 测试者里，在学期初期就depressed的，相比起那些没有depressed的，之后直到学习结束也不是很有可能开始吸烟。

也就是说，这道题题目的出结论是：很有可能是吸烟引起年轻人情绪沮丧。

而A是证明：不是年轻人情绪沮丧而导致抽烟。

这是我的看法。大家提意见！

问题问的是加强，照上层楼所说A应该是削弱才是，但是GWD给的答案是A，我看了半天也不明白。

再次请教。

题目说：开始吸烟&更加depressed同时发生=>吸烟导致depressed)

所以可以有3种结果：1）吸烟=>depressed跟题目预测一样

2）depressed=〉吸烟

3）depressed&吸烟由他因导致

A说depressed不会导致吸烟，就是否定了2），所以加强

如果选项否定3）同样也是加强，因为都使得1）可能性更大,或者前面一个描述(比如上升,下降)相反的一个状态呢?