GWD8-4

ANSWER:  C  I have researched this question, both here on ST and in the grammar/style texts, and I cannot find any support for D in this case (or, generally, as "of what" is simply poor style, even when it is not grammatically incorrect). This is a question that deals with correct usage of a relative pronoun (that, which, who, whom, what, and whose). The function of a relative pronoun is to introduce a subordinate clause and relate it to another antecedent word or idea. In this sentence, that idea is "...three times the price..." The relative pronouns which would work here are: that and which (not "what," not "of what, not "at which"). So, A, B, D, and E do not work with this construction. And, by the way, "of what" can nearly always be said in a better, more stylistically acceptable fashion. This sentence should read, "A new hair-growing drug is being sold for three times the price, per milligram, that the drug's maker charges for another product with the same active ingredient." The first part of the sentence is the main (or independent) clause. The last part of the sentence is the subordinate (or dependent) clause. "That" refers to "three times the price" clearly and it introduces the subordinate clause correctly. C is the best answer, FOR THIS CONSTRUCTION. If "the price" were omitted from the sentence, then this would be correct, "A new hair-growing drug is being sold for three times, per milligram, what the drug's maker charges for another product with the same active ingredient." But, even with this construction, "of what" does not work.