费费逻辑第50题—被充分必要条件整晕了

nickychen

Joseph: My encyclopedia says that the mathematician Pierre de Fermat died in 1665 without leaving behind any written proof for a theorem that he claimed nonetheless to have proved. Probably this alleged theorem simply cannot be proved, since---as the article points out---no one else has been able to prove it. Therefore it is likely that Fermat was either lying or else mistaken when he made his claim.

Laura: Your encyclopedia is out of date. Recently someone has in fact proved Fermat’s theorem. And since the theorem is provable, your claim---that Fermat was lying or mistaken---clearly is wrong.

50. Which one of the following most accurately describes a reasoning error in Laura’s argument?

(A) It purports to establish its conclusion by making a claim that, if true, would actually contradict that conclusion.

(B) It mistakenly assumes that the quality of a person’s character can legitimately be taken to guarantee the accuracy of the claims that person has made.

(C) It mistakes something that is necessary for its conclusion to follow for something that ensures that the conclusion follows.

(D) It uses the term “provable” without defining it.

(E) It fails to distinguish between a true claim that has mistakenly between believed to be false and a false claim that has mistakenly been believed to be true.

答案选C，解释上说是必要条件不充分，是说有人解出来了是F解出来的必要条件，但不一定有人解出来了就一定是F解出来的意思吗？在考试中，真的有时间并且要不断思考这是必要条件还是充分条件吗？必要条件和充分条件用英文都可以怎么表达啊...不然想明白了好像也选不出来...

大家还有什么关于充分必要条件的好例题分享一下的吗？好像OG上面没有类似的...非常感谢！！

nickychen

自己顶一下 有对充分必要有研究的大侠请指点！