-1-1-16. 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.

answer:C  not+weaken

典型的排除他因. 原文认为是严格的新规章使得mechanical problem被更多的检测出来. 言下之意是mechanical problem本身并没有同幅增长. 而C就是这个意思, 既不是因为mechanical problem本身增加了50%造成的. 这类题目的题干为:A-->B, assumption: 不是C-->B