[讨论]大全-2-20

XDF-CR -section 2-19,20
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.
(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 conse-quences 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.
(E) The number of prospective first-time donors is likely to go up by 5 percent.

For 20, anwser D depends on the assumption that the number of people want to donate blood does not increase and the blood usage does not decrease.
However, if we assume people catch NANB if and only if through blood transfer (however unreasonable this assumption is), then (A) can be inferred.

I know this might sound like 胡搅蛮缠，even though I do not think (A) is correct, I don't think (D) is much better. As said, it depends on the assumption that the number of people go to screening does not increase, which I don't think you can infer from the question.

So, 你怎样把握哪些additional assumption is reasonable, which are not ?