为什么选c啊 谁能解释此题

brianfang

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.

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红尘道士

用that定语从句修饰price

CharieBrown

the drug's maker charges ( the price) for another product with the same active ingredient

从句结构不完整