Blood banks will shortly start to screen all donors for NANB hepatitis. Although the new screening testes 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.

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

B) Donors carrying NANB hepatitis do not, in 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.

此题答案是Ａ，　偶不太理解，请哪位高人帮助解释一下，先谢过了

将选项取非放入原文，如果削弱了，则选项本身就是假设。故A选项正确。但我不明白的是E为何错？如果患肝炎的人献血的频率和正常人不一样，血样的感染率和患肝炎的感染率也就不一样啊。请指教

题目的假设就是donors carrying NANB hepatitis不会因为携带其他病毒 而被检测出来排除在捐献之外，否则题目中的计算公式就不成立~