请教XDF补充教材1道, 难道XDF的答案有误？

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.

(E) The donors who will still supply NANB-contaminated blood will donate blood at the average frequency for all donors.

XDF给的正确答案是A？ 不知道真的正确与否，盼简单解释，谢谢！

E should be the answer

b/c if those donors with NANB-contaiminated blood  donate less frequently than all donors, maybe they simply don't come next time, and as a result, no more than 10 percent of the population will still supply the NANB-contaiminated blood  as claimed by the argument. Then the argument would not stand, and so E must be assumed.

A is not even related.

This question doesn't seem like a good one:

While the argument itself does not give the information, the assumption in choice A suddenly mentions other infections for which reliable screening tests are routinely performed. Hence, my original reaction is, hey, this thing is not mentioned, and of course is not related.

Anyway,the original argument should look like this:

Besides running the current tests for several different deseases, 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.

I don't think ETS will give a test like that.

排除他因 or not, in a real ETS test, more or less the argument itself will give you a hint.  According to choice B, we know that there are other screening tests available, but we don't know whether the organization is going to use them or not. So this kind of information is often mentioned in the context in a real ETS test. 

Give you an example:

According to the law in country X, all the parents' properties should be passed to their children after they die. Since her parents just passed away, she is going to get 100% of their properties.

what do you think the assumption should be? It should be like the following:

Her parents didn't have other children.
 

But the XDF assumption is like this:

Her brothers and sisters would give up their shares of  the proerties.

Now, you can judge what should be added to the orginal context in order to make the XDF way of assumption:

She is one of the 5 children in the family. According to the law in country X, all the parents' properties should be passed to their children after they die. Since her parents just passed away, she is going to get 100% of their properties.

Hence, without the informtion added, we can't take it for granted that other tests are going to be run by the blood bank, even though those tests are available.

My conclusion:

This question by XDF is not a good one.