[求助]GWD17-16

舟子哥

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?

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.

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.

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

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

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

   Answer:

lyle

B，应该算是保持样本不变，也算排除他因吧。

captain_seu

我认为是A， 原因是A选项排除了那些已经在学习上处于被动的样本，那么就更加能够说明：那些在学习上主动的人因为抽烟，在学习末了容易被动。

yangxiaogang

A is the key. it rules out another explanation

XHuang4

取非的方法应该好解释一点。

A，说郁闷的小孩和那些不郁闷的小孩抽烟的可能性一样。取非就是说郁闷的小孩更有可能抽烟——郁闷导致抽烟。文章结论说，抽烟导致郁闷。正好是相反了；

B，说一开始抽烟的小孩和那些中途开始抽烟的小孩，最后退出抽烟的可能性都一样，取非以后和文章结论没有关系；

C，D，E类似可以排除。

lyle

原来如此。

阿彻

这题是排除法