23. On a certain day, nine scheduled flights on Swift Airlines were canceled. Ordinarily, a cancellation is due to mechanical problems with the airplane scheduled for a certain flight. However, since it is unlikely that Swift would have the mechanical problems with more than one or two scheduled flights on a single day, some of the nine cancellations were probably due to something else.
The argument depends on which one of the following assumptions?
A. More than one or two airplanes were scheduled for the nine canceled flights.
B. Swift Airlines has fewer mechanical problems than do other airlines of the same size.
C. Each of the canceled flights would have been longer than the average flight on Swift Airlines.
D. Swift Airlines had never before canceled more than one or two scheduled flights on a single day.
E. All of the airplanes scheduled for the canceled flights are based at the same airport.
参考答案：A 采用取非法。
思路：否定More than one or two airplanes were scheduled for the nine canceled flights.将削弱作者的结论。
A：取非削弱
B：无关。
C：无关。
D：无关。
E：无关。
俺用排除法选对了，但是不是很明白为什么是这个答案。费费上的解释也不很清楚，请NN们指点～～～～ | 
