看不明白的题目

Although the ratio of physicians to total populationis

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 assuption 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 US is not larger than that of Canada.

C)US patients sometimes travel to Canada for certain kinds

   of surgery.

D)general practitioner in the US do not as a rule examine a patient

   who is a candidate for surgery before sending the patient to a 

  surgeon.

E)there are no unnecessary surgical operations performed in Canada.

你们选什么？

我连题目都不明白，前提？？结论？？都找不出来！

Ａ．

题目：美国和加拿大在人口一样的情况下，按照平均人口计算美比加外科大夫多３３％，因此按照平均人口计算，美手术比加多４０％

前提：医生多，结论：手术多

Ａ取非导致题目不成立

如果美国患者对手术的需要比加拿大患者多就会使得人均手术比下降？？

我对取非还是不太解。

很清楚了。

谢谢！