hair growth

[sq720]

A new hair growth drug is being sold for three times teh price, per milligram, as the drug's maker charges for another product with the same active ingredient

as
than
that
of what
at which

why is B not correct
ans C

[nillss]

Think about this...
if the drug's maker charges Rs. 30 for another product with the same active ingredient , then this new hair growth drug is being sold for three times the price of the other product. now try to fit in 'that' ( price)