请教各位大侠，对OG 172的疑问

172. There is a great deal of geographical variation in the frequency of many surgical procedures—up to tenfold variation per hundred thousand between different areas in the numbers of hysterectomies, prostatectomies, and tonsillectomies.

To support a conclusion that much of the variation is due to unnecessary surgical procedures, it would be most important to establish which of the following?

(A) A local board of review at each hospital examines the records of every operation to determine whether the surgical procedure was necessary.

(B) The variation is unrelated to factors (other than the surgical procedures themselves) that influence the incidence of diseases for which surgery might be considered.

(C) There are several categories of surgical procedure (other than hysterectomies, prostatectomies, and tonsillectomies) that are often performed unnecessarily.

(D) For certain surgical procedures, it is difficult to determine after the operation whether the procedures were necessary or whether alternative treatment would have succeeded.

(E) With respect to how often they are performed unnecessarily, hysterectomies, prostatectomies, and tonsillectomies are representative of surgical procedures in general.

这题就是想找多一个支持结论的前提条件出来

答案选B，解释说To establish that much of the variation is due to unnecessary surgical procedures, it is necessary to eliminate the possibility that the geographical variation reflects variation in the incidence of disease treated with these procedures. Choice B, if established, would eliminate this possibility and is thus the best answer

这个说法我同意，属于否定他因的老套路。

但是E为何不对呢？解释说Neither C or E bears on the conclusion, since neither the conclusion nor the cited geographical variation involves procedures are of the kind D describes, the difficulty of determining an individual operations’ necessity would merely increase the difficulty of verifying the suggested conclusion. 这都是哪跟哪啊？