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.
Why the answers are A, D
这道题记得是讨论过的.
1. A is a support. 如果disqualify up to 5 percent of all prospective blood donors 中含有some people from two-thirds of donors carrying NANB hepatitis, 那么结论about 10 percent of actual donors will still supply NANB-contaminated blood就推不出了, 可能是<10% actual donors will still supply NANB-contaminated blood. 其他对结论没有支持作用.
2. D说明the new screening tests 会起到的作用,和the new screening tests are estimated to disqualify up to 5 percent of all prospective blood donors的叙述一致
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