A tank has three pipes P, Q and R. The pipes P and fill it independently in 4 hours and 5 hours respectively while R empties it in 2 hours. If P. Q and R are respectively opened at 1 AM, 2 AM and 3 AMinthat order. then the time when the tank will be empty is

A

4 PM

B

5 PM

C

6 PM

D

7 PM