Fei Fei 61 -- 已查过讨论贴，链接均在，仍有疑问...

61. Investigators concluded that human failure was not responsible for the fatal airplane crash last August, and since that time new and more stringent rules for identifying and reporting mechanical problems have been in effect. That accounts for the fact that reports of airplane mechanical problems have increased in frequency by 50 percent since last August. 

 Which one of the following is an assumption underlying the argument in the passage? 

A.       Airplane travel is still relatively safe, despite the increase in reported mechanical problems. 

B.        Mechanical problems in airplanes have increased dramatically since last August. 

C.        Mechanical problems in airplanes have not increased by 50 percent since last August. 

D.       Airlines are less reluctant to report mechanical problems than they previously were. 

E.        Mechanical problems in airplanes have become easier to detect since last August. 

前辈讨论贴如下:

http://forum.chasedream.com/dispbbs.asp?BoardID=24&ID=45830&replyID=&skin=1

http://forum.chasedream.com/dispbbs.asp?BoardID=24&ID=21629&replyID=&skin=1

http://forum.chasedream.com/dispbbs.asp?BoardID=24&replyID=1841424&id=196084&skin=0

http://forum.chasedream.com/dispbbs.asp?BoardID=24&replyID=1793658&id=190840&skin=0

好像NN们都是思路很清晰的找到C答案，不明白的是如果仅仅关注since last august之后的事情，那么第一句话讲last august的情况，在这题里起的是一个什么作用呢？就是这个时间关系把握搞晕了，看了半天题目也找不到思路.

请NN指点谢谢！

这题应该算是最难的那种题目。不过似乎有不少题目都是和这题很相似的，换汤不换药。

首先看到那个account for要警觉，account for表示了前后有因果关系，前因，后果。

然后最好能自己明确一下具体什么是因，什么是果。这里的因是new and more stringent rules for xxx. 果是frequency of reports上升了50%。

最后一步看选项，能直接看出来最好，但这题难在C直接看有点不一目了然，需要把C的否命题代到段落里试验，如果也能得到原结论的否命题，就说明C是一个必要条件。即 否C=>否A <=> A=>C。两个互为逆否，故等价。如果C是命题的必要条件，C就是命题的一个assumption。

他因削弱题，另外一个原因（Mechanical problems in airplanes have increased by 50 percent since last August）是可以解释 reports of airplane mechanical problems have increased in frequency by 50 percent since last August的，如果前一个解释成立，那argument就不成立了。注意选项是作者基于的基础。

所以基础就是Mechanical problems in airplanes have not increased by 50 percent since last August，即他因不存在即 非A - B 不成立。

这道题难在“ 非A ”的确认很难，如果C选是“Mechanical problems in airplanes 将准确反映在Report上，而且是不得而知的” 这和C选项效果对等，我想应该就会好选很多吧

谢谢两位指点！

可能我需要做的是不关注细节，而是关注段话的逻辑关系。