gwd-4-4 查过资料，答案都未能统一……

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.

as
than
that
of what
at which

XY给出c，讨论是d，首先答案我就不明确，其次更不知道为什么……大家给我讲讲吧……

我把中间的插入语拿掉你看是不是比较清楚了。

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

ft so easy now ....

so the answer is C~~

thanks a million carol, not only for this one, but also for all the patient explanations!