prep08的题目，，拜托啦~~~~

宝爱一

A new hair-growth 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

这道题选C，可是that不是引导非限么，前面能加逗号么！！！求NN解惑啊~~~~

mslancaster

which引导non-restrictive
that引导restrictive

这里出现逗号是因为per milligram是插入语

宝爱一

got it~~~