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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。
不是很明白这道题的思路，文中说，现象：有九班航班在一天之内被取消。解释：通常航班取消是因为承担该次航班的飞机有机械故障，而一天之内超过两个航班有机械事故的概率很小。结论： 九班航班取消中一定有不是因为机械故障而取消的。
正确答案为A：取消的九个航班是由不止一两个飞机承担的。
取非为：取消的航班都是由一个或两个飞机承担的。
这是怎么削弱的原题结论的呢？请大家点拨一下～～ |
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发表于 2010-4-4 13:13:05
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