请教涛涛GWD8-4

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.

1. as

2. than

3. that

4. of what

5. at which

为什么选D啊,C为什么不对呢，谢谢

C

that修饰price 觉得挺好的

不知道为什么选D 同问

我选C.理由：

1. per milligram是插入语，that后的从句不会错误修饰它，而能清楚地修饰price.

2.  of what中的what的作用和price重复，如果用what 这个句子可以改为

A new hair-growing drug is being sold for three times what the drug’s maker charges for another product with the same active ingredient.

A new hair-growing drug is being sold for three times what the drug’s maker charges for another product with the same active ingredient.