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.

不理解文章的意思啊!为什么选A呢!先谢谢了

血库测试献血者是否有肝炎.虽然新的测试方法取消了5%的潜在献血者的资格,仍漏掉了三分之二的有肝炎的人,结论:所以大约有10%的有肝炎的人还在献血.

想不通为什么A是假设??

这更像一道数学题，总人数的5%排出，但仍有2/3的肝炎携带者没排出，若1/3的肝炎携带者占总人数的5%，那么所有肝炎携带者占15%，排了5%，还剩10%。

所以假设就是肝炎携带者的1/3被排（被测出）就行了。

a有此意。