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.
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.
I am not sure. longman doesn't explain this "charge for" in detail. But a example in kingsoft, "charges ten dollars for a haircut", may lend some support to choice C.
很巧,刚看了这个帖子就在阅读中看到一个例子,63-9-Question8-D:Many directors of large firms believe that the government should establish the prices that will be charged for products.