| 请教一道gwd的语法-13-8
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.
price of what感觉有些不对头。请大家指点！感谢！ | 
