Q18: GWD-4-4

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.      as

B.       than

C.      that

D.      of what

E.       at which

给的答案是选C， 怎么也看不明白，请给位给点拨一下，谢谢~~~~

固定搭配：charge (a price，数额) for sth.

three times sth.三倍的某物

three times the price that the drug’s maker charges for another product with the same active ingredient

that引导定语从句，先行词为the price，定语从句中，that做charge的宾语

刚查了下语法书
基数词 + times + as + 形容词/副词原级 + as 。。。
基数词 + times + 形容词/副词比较级 + than 。。。
基数词 + times + the + 表示大小或数量的名词（如size，length等） + of 。

。。

那这题是不是考的是第三种用法？应该选D阿