求助XDF蓝宝书P111Q289

Critics of sales seminars run by outside consultants point out that since 1987， revenues of vacuum cleaner companies whose employees attended consult ant-led seminars were lower than revenues of vacuum cleaner companies whose employees did not attend such seminars。 The critics charge that for vacuum cleaner companies， the sales siminars are ill conceived and a waste of money。 Which of the following，if true，is the most effective challenge to the critics of sales seminars？

A   Those vacuum cleaner companies whose sales were highest prior to 1987 are the only companies that did not send employees to the seminars。

B   vacuum cleaner companies that have sent employees to sales seminars since 1987 experienced a greater drop in sales than they had prior to 1987。

C   The cost of vacuum cleaner sales seminars run by outside consultants has risen dramatically since 1987。

D   The poor design of vacuum cleaner sales seminars is not the only reason for their ineffectiveness。

E   Since 1987， sales of vacuum cleaners have risen twenty percent。

Answer：A   答案居然是A哦。。。各位不要怀疑答案正确性，记得XDF老师上课时讲过这题，只是现在怎么也想不明白了。。。希望大N指点

看到CRITICS,SURVEY，直接联想到调查范围有问题。

参加S收入反而比没有参加S的收入来的小，结论S无用。

削弱：不是S无用，而是其他原因。

找他因：A 唯一没参加的人是行业领头羊，

B 加强C扯远了D加强E无关。

哦。。。明白了。。。原来是横向比较，先前一直以为是纵向比较了呢。。。呵呵~

谢谢楼上！