[求助]几道逻辑题求解释，谢谢！

1，Six months or so after getting a video recorder, many early buyers apparently lost interest in obtaining videos to watch on it. The trade of businesses selling and renting videos is still buoyant, because the number of homes with video recorders is still growing. But clearly, once the market for video recorders is saturated, businesses distributing videos face hard times.fficeffice" />

Which of the following, if true, would most seriously weaken the conclusion above?

(A) The market for video recorders would not be considered saturated until there was one in 80 percent of homes.

(B)    Among the items handled by video distributors are many films specifically produced as video features.

(C) Few of the early buyers of video recorders raised any complaints about performance aspects of the new product.

(D) The early buyers of a novel product are always people who are quick to acquire novelties, but also often as quick to tire of them.（D）

(E) In a shrinking market, competition always intensifies and marginal businesses fail.

D为什么对，是什么思路？

Questions 19-20 are based on the following.

Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors, they will still miss two-thirds of donors carrying NANB hepatitis. Therefore, about 10 percent of actual donors will still supply NANB-contaminated blood.

19.         ★The argument above depends on which of the following assumptions?

(A) Donors carrying NANB hepatitis do not, in a large percentage of cases, carry other infections for which reliable screening tests are routinely performed.

(B) Donors carrying NANB hepatitis do not, in a large percentage of cases, develop the disease themselves at any point.

(C) The estimate of the number of donors who would be disqualified by tests for NANB hepatitis is an underestimate.

(D) The incidence of NANB hepatitis is lower among the potential blood donors than it is in the population at large.（A）

(E)             The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

20.         ★Which of the following inferences about the consequences of instituting the new tests is best supported by the passage above?

(A) The incidence of new cases of NANB hepatitis is likely to go up by 10 percent.

(B) Donations made by patients specifically for their own use are likely to become less frequent.

(C) The demand for blood from blood banks is likely to fluctuate more strongly.

(D) The blood supplies available from blood banks are likely to go down.（D）

(E) The number of prospective first-time donors is likely to go up by 5 percent.

这个题目我怎么也读不懂，其中的5%和2/3还有10%之间是什么关系，我根本不知道题目在说什么，请求解释，谢谢！