A decrease in face-to-face social contact can precipitate depression. Time spent using the Internet cannot be spent in face-to-face social contact, so psychologists have speculated that sharply increasing Internet use can cause depression. Studies of regular Internet users have found a significantly higher incidence of depression among those who had recently doubled the amount of time they spent using the Internet than among those whose use had not increased. Hence, the psychologists’ speculation is correct.
1. Which of the following is an assumption on which the argument depends?
A. In general, the reason that the people in the studies had doubled their Internet use was not that they had earlier experienced a significant decrease in opportunities for face-to-face social contract.
B. A sharp decrease in face-to-face social contact is the only change in daily activity that can lead to an increased incidence of depression.
C. Using the Internet presents no opportunities for people to increase the amount of face-to-face social contact they experienced in their daily lives.
D. Regular Internet users who are depressed will experience an immediate improvement in mood if they sharply decrease the amount of time they spend on the Internet.
E. Before they doubled the time they spent on the Internet, the people who did so were already more prone to depression than are regular Internet users in general.
答案：C
解析：题目问文章论证基于的假设。
文章中心结论是中间这句：so psychologists have speculated that sharply increasing Internet use can cause depression 增加上网时间会引起抑郁。
文章理由以该句结论为界，分为前后两个部分：前半部分理由看起来是一个链状推理：减少面对面社交会引起抑郁。用来上网的时间不能用于面对面社交。后半部分理由是一个对比研究：最近增加两倍上网时间的常规网络用户比没有增加的常规网络用户有更高的抑郁发生率。前后两半部分理由到结论各需要什么假设?或者，各自推理在何种情况下会不成立?
先说后半部分。这个对比研究支持结论需要什么假设?对啦?实验前、实验中没有其他干扰变量啦!
前半部分呢?看出来了么?它貌似一个链状推理，但它与严密支持结论的链状推理之间是有出入的。
这样一个链状推理才是严密的，无懈可击的：
理由1：减少面对面社交会引起抑郁
理由2：增加上网的时间会减少面对面社交时间
结论：增加上网时间会引起抑郁
对啦!问题是：即使用来上网的时间不能用于面对面社交，但是否能增加每天其他时间的面对面社交机会呢?比如，俺上网用来dating, 上网之后意犹未尽，相约面对面热聊啦!如果出现这种情况，原文推理就不是我们需要的严密推理啦!所以，文章推理依据的假设就是要排除这种情况。就是C选项啦!
至于你所纠结的B选项，原文推理只需要一个充分条件：减少面对面社交一定会引起抑郁，不需要B选项所表达的必要条件啦!
还有，A选项是针对文章中哪一部分推理?对啦!后半部分!后半部分对比研究到结论不需要这个假设，为什么?如果你想明白，就不用再参加什么培训啦!你对GRE阅读，至少是逻辑单题部分理解已经很到位啦!
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