XDF网络课堂第5讲2题

summersmile

第5讲


8.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 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.



13.Y has been believed to cause Z. A new report, noting that Y and Z are often observed to be preceded by X, suggests that X, not Y, may be the cause of Z.Which of the following further observations would best support the new report's suggestion?



(A) In cases where X occurs but Y does not, X is usually followed by Z.
(B) In cases where X occurs, followed by Y, Y is usually followed by Z.
(C) In cases where Y occurs but X does not, Y is usually followed by Z.
(D) In cases where Y occurs but Z does not, Y is usually preceded by X.
(E) In cases where Z occurs, it is usually preceded by X and Y.


8 答案A             13 答案A    


13：不明白D，大家是怎么分析此题的？noting that Y and Z are often observed to be preceded by X,这句在逻辑分析中起什么作用，是否应略去不读？


8： feiei说the new screening tests 与A选项的reliable screening tests 不是同一概念，不明白，我认为是一样的。

weiyu

8. 是排除他因．即其它因素不再导致被screen out.


13. 要证明X->Y,Z. 而Y不是Z的原因，只能是A．Y没发生，X->Z

summersmile

thanks. 但还是不明白8: 我认为只有the new screening tests 与A选项的reliable screening tests 是指同样的tests,才能是排除他因。但feifei说不是，这样不就不是排除他因了吗？