请指教哦！

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 attended such seminars. The critics charge that for vacuum cleaner companies, the sales seminars 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 only companies that did not send employees to the seminars.

(D) the poor design of vacuum cleaner sales seminars is not the only reason for their ineffectiveness.

请问这道题的讨论链接在哪里？我确实找不到。

答案为A，怎么会用一个时间对不上的选项（即使内容再对，时间不在同一个时期就应该不对呀！）答案，请指教？

我选的是D，如果错，错在哪？

谢谢！

请给出题目的出处吧。

应该是A

事实：与会公司的revenue比未与会公司的revenue低

结论：会没有用

削弱：无因有果：1987年前的highest的公司并没有参与研讨会，但是他们还是没落了。

      这说明与会与否与revenue必然联系，得不出这个结论。

D：题目问得是对seminar批评的挑战（削弱），D感觉无关。。。

不知道nn怎么看？