18. Critics of
sales seminars run by outside consultants point out that since 1987, revenues
of vacuum cleaner companies whose employees attended consultant-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 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 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.（A）
(E) Since 1987, sales of vacuum
cleaners have risen twenty percent.
Key: A
按照A的解释不是有力地支持了critics of sales seminars的结论了吗？怎么是challenge呢？ | 
