A new hair-growing drug is being sold for three times the price, per milligram, as the drug’s maker charges for another product with the same active ingredient.
as
than
that
of what
at which
我觉得应该选C,that作price的定语,就是the price that the manufacturer charges for another product.
obviously, it took one year to discuss this item and most of GMATers vote for C. NN, who can tell what is wrong with E since i'm not alone to ask this?