Critical Reasoning

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

I really like CR questions, but for some reason I never seem to be that good in CR...
Anyway, here's my opinion;

A is out since we're only interested in sinus pain effectiveness.

D is out, since the availability of Novex is not discussed; you're only interested in its effectiveness

E is out since it actually strengthens the conclusion that Novex is an effective drug (since it performed better than the competing brands of painkillers).

We're left with B and C. While C was my initial guess, after re-reading the passage I'd go for B. They both sort of provide explanations to why the majority of hospitals use Novex:
B - patients don't tolerate other painkillers
C - hospitals save money - BUT here's the trap: many drug manufacturers do try to sell their products at a discount, but that doesn't necessarily mean that Novex manufacturers do the same

What is the OA?