A study followed a group of teenagers who had never smoked and tracked whether they took up smoking and how their mental health changed. After one year, the incidence of depression among those who had taken up smoking was four times as high as it was among those who had not. 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?
A. Participants who were depressed at the start of the study were no more likely to be smokers after one year than those who were not depressed.
B. The study did not distinguish between participants who smoked only occasionally and those who were heavy smokers.
C. Few, if any, of the participants in the study were friends or relatives of other participants.
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.
正确答案：A
我的问题：E为什么不可以？虽然E有无关的风险，但若理解为它因，即depression是因为alcohol引起的，否定了它因，为什么不能strengthen结论？谢谢
这题目有些怪异，按照答案推理，这道题更像是“assumption"题。因为答案A实际上是说结论的出现是建立在答案A的基础之上的。
尽管如此，我们仍然可以很轻易地排除E, 因为E既然说depression是由酒精引起的，就否定了“尼古丁是罪魁祸首”的结论。是典型的削弱。你必须找到“支持尼古丁是引起抑郁的原因”的选项才能支持结论。
我没看过新东方的什么指导，但很显然，你运用所谓“否定它因”是误导了自己。
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