Task: Question Answering
Input (English): Question: Pumps A, B, and C operate at their respective constant rates. Pumps A and B, operating simultaneously, can fill a certain tank in 2 hours; pumps A and C, operating simultaneously, can fill the tank in 1 hours; and pumps B and C, operating simultaneously, can fill the tank in 2 hours. How many hours does it take pumps A, B, and C, operating simultaneously, to fill the tank.

 Option A: 1/3

 Option B: 1/2

 Option C: 1/4

 Option D: 5/2

 Option E: 5/6
Output (English): Option D