一道很有意思的题：新东方蓝书#44

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.

The argument 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.

a是答案。

可我觉得a貌似不完整，因为剩下的85%的donor中患“other infections”比例未知。如果其他donor也有相同或相近的比例患“other infections”，那么最后actual donor中NANB携带者的比例不还是能维持在10%左右吗？