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 as 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?
说一群砖家对一批青少年进行一年的跟踪研究，发现那些在研究开始的一个月内开始养成吸烟习惯的青少年比一直没吸烟的抑郁概率大四倍。结论是香烟中的尼古丁会对大脑化学成分产生影响进而影响情绪，所以吸烟会导致抑郁。问哪个增强了结论。
A：研究样本中那些一开始就抑郁的人并没有比从来不抑郁的人更容易染上吸烟习惯。（取否：一开始就抑郁的人比不抑郁的人更容易染上吸烟习惯，则推得是抑郁导致吸烟，而不是吸烟导致抑郁，取否是大大削弱的，故A本身增强了结论。）
B：那些研究开始一个月内就染上吸烟习惯的人并没有比研究中期才染上吸烟习惯的人更倾向于能在研究结束时把烟戒了。（跟抑郁无关）
C：一看就无关
D：一些参与者在整个研究过程中经历了进入抑郁再脱离抑郁的过程。（不是很确定emerge from的意思，反正也无关）
E：研究把酗酒问题排除在外了（无关）
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