费费第二部份19题

Although the ratio of physicians to total population is about the same in the United States and Canada, the United States has 33 percent more surgeons per capita. Clearly, this is the reason people in the United States undergo 40 percent more operations per capita than do Canadians.
The explanation given above rests on an assumption that
(A) patients in the United States do not have a greater need for surgery than do patients in Canada
(B) the population of the United States is not larger than that of Canada
(C) United States patients sometimes travel to Canada for certain kinds of surgery
(D) General practitioners in the United States do not as a rule examine a who is a candidate for surgery before sending the patient to a surgeon.
(E) There are no unnecessary surgical operations performed in Canada.

正确为A,看不懂D选项，不知能否有人解释一下？谢谢

A是很明显的否定削弱的假设项，XDF教过的说。

D我一看就认为无关，根本没看，也看不懂的说。

请问有没有人可以解释一下D的结构是怎么出来的呀？

自己顶

还有一个问题，有谁可以解释一下位啥么答案选A吗？