请教GWD TN 24: 第三套，第18题

qianyangnet

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

答案是C

为啥啊？谢谢！

dhr945

per milligram 是插入语，这样that引导price的定语从句～

qianyangnet

谢谢!

但请问A和D为什么错呢？