求助：xdf 绿皮书 44题

milanmilan

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

ethyl

LZ可以在逻辑大全里面搜到此题的题号，然后去本区置顶的讨论汇总帖里面查找讨论，岂不很便捷？

yangxiaogang

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

bedroom

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~

此题为大全2-19，楼主不妨自己搜搜前人的讨论看看

milanmilan

嘻嘻 原来老早就有人问过拉   

from robertchu ： Q19: please refer to http://forum.chasedream.com/dispbbs.asp?boardID=24&ID=55690&page=1

如果有ＮＡＮＢ的人也有别的毛病，而且会因为这些别的毛病被剔除，那么他们就不会被献血．那么ＮＡＮＢ血的比例就不合高到10%

from siebel 19. 数学推导可得，about 10 percent of actual donors will still supply NANB-contaminated blood.

答案A表明：有病捐血者不会因为其他原因而被排除在外。即：没有其他可能使这个10%降低，当然就是原题的assumption了。

多谢楼上各位指教

[此贴子已经被作者于2005-10-1 21:58:33编辑过]