In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: two pipes a and b can separately fill a tank in 12 and 20 minutes respectively . a third pipe c can drain off 45 liters of water per minute . if all the pipes are opened , the tank can be filled in 15 minutes . what is the capacity of the tank ? 
Options: a ) 542 , b ) 540 , c ) 675 , d ) 829 , e ) 279
Example Output: c

Example Input: Problem: how many seconds will a 1200 m long train take to cross a man walking with a speed of 3 km / hr in the direction of the moving train if the speed of the train is 63 km / hr ? 
Options: a ) 26 sec , b ) 65 sec , c ) 55 sec , d ) 19 sec , e ) 72 sec
Example Output: e

Example Input: Problem: the speed of the boat in still water in 12 kmph . it can travel downstream through 42 kms in 3 hrs . in what time would it cover the same distance upstream ? 
Options: a ) 8 hours , b ) 6 hours , c ) 4.2 hours , d ) 5 hours , e ) 6 hours
Example Output:
c