最近发现自己的逻辑思路比较怪异，都是看了充分必要条件惹的祸，求解

Joseph_lin

Althoughcomputerscanenhancepeople'sabilitytocommunicate,computergamesareacauseof
underdevelopedcommunicationskillsinchildren.After-schoolhoursspentplayingcomputergamesare
hoursnotspenttalkingwithpeople.Therefore,childrenwhospendalltheirsparetimeplayingthesegames
havelessexperienceininterpersonalcommunicationthanotherchildrenhave.

Theargumentdepends[Y1]onwhichofthefollowingassumptions?

(A)Passiveactivitiessuchaswatchingtelevisionandlisteningtomusicdonothinderthedevelopmentof
communicationskillsinchildren.

(B)Mostchildrenhaveotheropportunities,inadditiontoafter-schoolhours,inwhichtheycanchoosewhether
toplaycomputergamesortointeractwithotherpeople.

(C)Childrenwhodonotspendalloftheirafter-schoolhoursplayingcomputergamesspendatleastsomeof
thattimetalkingwithotherpeople.

(D)Formalinstructioncontributeslittleornothingtochildren'sacquisitionofcommunicationskills.

(E)Thementalskillsdevelopedthroughplayingcomputergamesdonotcontributesignificantlytochildren's
intellectualdevelopment.

这道题目很简单，答案是C，我最近看了一些是充分必要条件的题目，估计还没掌握得当，发现有些题目用充分必要条件来看就会不对，我估计是我思维上出了问题，请大家帮忙分析分析我错在哪里？
由这道题目可以得出:  打游戏----->不和人沟通了   我们把打游戏看做是A，不和人沟通看作是B，那么结论是(A---->B)，再看C的这个答案，是(否A--->否B)，那么它逆否命题是(B---->A)，这样不就和原结论正好倒了一下，原来结论中的A是充分条件，而现在A却变成了必要条件，不是就不对了么？我不知道我的思维过程错在了哪里，不知道哪位大侠可以帮忙分析下？

另外，我们平时在做假设题中，很多都是因果关系的题目，因果关系是充分必要关系吗？如果是的话，如果结论是(A--->B)，那么我假设题的答案是不是只能是(A--->B)和(否B--->否A)呢？

Joseph_lin

UP

lostkitten

所以说没学过集合论和数学逻辑不要轻易看看这些技巧就做题。
Children who do not spend all of their after-school hours playing computer games spend at least some of
that time talking with other people.说的是(not A---->not B)吗？不是
是(not B---->not A)
因为Children who do not spend all of their after-school hours playing computer games spend at least some of
that time说明不玩游戏的除了 talking with other people还可能干别的，因此 talking with other people才是subset，因此只能更具general rule axiom推理出(not B---->not A)。
是不是非常不实用？
最实用的方法就是排他因

zcy9079

是为啥。。。。

zcy9079

顶个

sdcar2010

Necessary assumption. Use negation.

If you negate C, you get:
Children who do not spend all of their after-school hours playing computer games spend NO time talking with other people.
If this is the case, the conclusion that "those who play games have less experience in interpersonal communication than those who don't" will fall apart. So C is the necessary condition.

Joseph_lin

UP

Joseph_lin

题目是OG12-50,不好意思，题目在2楼，1楼的题目都没空格

Joseph_lin

Although  computers  can  enhance  people's ability to communicate, computer games are a cause of
underdeveloped communication skills in children. After-school hours spent playing computer games are
hours not spent talking with people. Therefore, children who spend all their spare time playing these games
have less experience in interpersonal communication than other children have.
The argument depends on which of the following assumptions?
(A)    assive activities such as watching television and listening to music do not hinder the development of
communication skills in children.
(B)    Most children have other opportunities, in addition to after-school hours, in which they can choose whether
to play computer games or to interact with other people.
(C)    Children who do not spend all of their after-school hours playing computer games spend at least some of
that time talking with other people.
(D)    Formal instruction contributes little or nothing to children's acquisition of communication skills.
(E)    The mental skills developed through playing computer games do not contribute significantly to children's
intellectual development.