重发求助feifei50（之前忘了把题目贴上，不好意思）

ran2010zx

Joseph: My encyclopedia says that themathematician Pierre de Fermat died in 1665 without leaving behind any writtenproof for a theorem that he claimed nonetheless to have proved. Probably thisalleged theorem simply cannot be proved, since---as the article points out---noone else has been able to prove it. Therefore it is likely that Fermat waseither 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Laura: Your encyclopedia is out of date.Recently someone has in fact proved Fermat’s theorem.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 isprovable, your claim---that Fermat was lying or mistaken---clearly is wrong.
50. Which one ofthe following most accurately describes a reasoning error in Laura’s argument?

A.      It purports to establish itsconclusion by making a claim that, if true, would actually contradict thatconclusion.
B.       It mistakenly assumes that thequality of a person’s character can legitimately be taken to guarantee theaccuracy of the claims that person has made.
C.       It mistakes something that isnecessary for its conclusion to follow for something that ensures that theconclusion follows.
D.      It uses the term “provable”without defining it.
E.       It fails to distinguish betweena true claim that has mistakenly between believed to be false and a false claimthat has mistakenly been believed to be true.
答案是C,可我觉得B对啊，而且C是神马意思都看不懂，求牛人指导！谢谢！！

Julie1983

http://forum.chasedream.com/GMAT_CR/thread-376671-1-1.html?SearchText=feifei 50

sdcar2010

B is totally irrelevant since a person's character is a red herring.

sdcar2010

Laura's premise is that the theory is provable. The fact that the theory is provable is necessary for the conclusion that Fermat has indeed proved the theory before his death. But this fact alone does not conclusively prove or sufficiently points out that Fermat has proved it. In other words, this fact alone is not a sufficient condition for the conclusion that Fermat has indeed proved the theory.

C points out this err in Laura's argument.