请教几道逻辑大全上的题？/大全-I-12,大全-I-18

大全-I-12 A newly discovered disease is thought to be caused by a certain bacterium. However, recently released data notes that the bacterium thrives in the presence of a certain virus, implying that it is actually the virus that causes the new disease.
Which of the following pieces of evidence would most support the data’s implication?
(A) In the absence of the virus, the disease has been observed to follow infection by the bacterium.
(B) The virus has been shown to aid the growth of bacterium, a process which often leads to the onset of the disease.
(C) The virus alone has been observed in many cases of the disease.
(D) In cases where the disease does not develop, infection by the bacterium is usually preceded by infection by the virus.
(E) Onset of the disease usually follows infection by both the virus and the bacterium.
answer：C ，B为什么不对？我觉得B是个很好的支持啊？

大全-I-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.
(E) Since 1987, sales of vacuum cleaners have risen twenty percent.
answer：A，为什么是A啊？我怎么觉得A像是一个支持的答案？