本人觉得C更正确一些，但不知道为什么正确答案是D呢，那位高人请指点一下啊！！

Advertisement: For sinus pain, three out of four hospitals give their patients Novex. So when you want the most effective painkiller for sinus pain, Novex is the one to choose.

Which of the following, if true, most seriously undermines the advertisement’s argument?

(A) Some competing brands of painkillers are intended to reduce other kinds of pain in addition to sinus pain.

(B) Many hospitals that do not usually use Novex will do so for those patients who cannot tolerate the drug the hospitals usually use.

(C) Many drug manufacturers increase sales of their products to hospitals by selling these products to the hospitals at the lowest price the manufacturers can afford.

(D) Unlike some competing brands of painkillers, Novex is available from pharmacies without a doctor’s prescription.（D）

(E) In clinical trials Novex has been found more effective than competing brands of painkillers that have been on the market longer than Novex.

这题的推理是：

医生给病人开N药多，所以N药的药效好。

D说的是N药是非处方药，所以开的多，一个他因削弱。

C只是说药商卖了更多的药给医院而已，只是对前提的说明，不在提干的推理范围内。

不知道这样解释你明白吗？