请教一道狒狒逻辑50题

风林火山

Questions 49-50
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Laura: Your encyclopedia is out of date.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.
答案学C，为什么呢？

changyou

C是必要条件当成了充分条件的意思，再随便说说，这样解释起来可能更明白……

风林火山

多谢你的解释，解释的很清楚。

teddyteddy

有人證明了理論，不代表F沒說謊，Laura的陳述忽略了他因的可能

myoka

Laura从“Recently someone has in fact proved Fermat’s theorem”推出“ Fermat was lying or mistaken---clearly is wrong.”

Fermat’s theorem is provable能推出Fermat was not lying or mistaken 吗?明显不可以咯~

“Recently someone has in fact proved Fermat’s theorem”就是c选项中的“something that is necessary for its conclusion”  只是necessary for the conclusion. but cannot ensure the conclusion.