Pipe A is a filling pipe while B and C are emptying pipes. Pipe A alone can fill the tank in 10 hours and pipe B alone can empty two-third part of the tank in 20 hours. If all the three pipes are opened together, the tank is completely filled in 40 hours. In how many hours can C alone empty two-third part of the tank?

A

24

B

12

C

16

D

20