Task: Question Answering
Input (English): Problem: pipe p can fill a tank in 2 hours , pipe q in 4 hours and pipe r in 12 hours . if all the pipes are open , in how many hours will the tank be filled ? 
Options: a ) 2 hours , b ) 1.2 hours , c ) 3 hours , d ) 1.5 hours , e ) 2.5 hours
Output (English): b