Without the presence of additional evidence or logic from an answer choice, the argument doesn't make complete sense. Lowering the cost of a drug doesn't necessarily mean that the seller of a drug would make "as much money as possible." The answer must explain why lowering the price would have this result, probably through drastically increased sales compared to the sales companies could expect if the prices were not lowered.

Sure enough, that's choice (C). It solidifies the logic that lowering the price leads to taking in more money, which is the drug companies' stated goal. The other choices are not as directly related to the narrow scope of the argument, which is such a key element of the correct answer choice is any Critical Reasoning question.