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: a can do a piece of work in 10 days . he works at it for 4 days and then b finishes it in 9 days . in how many days can a and b together finish the work ? 
Options: a ) 6 , b ) 7 , c ) 5 , d ) 4 , e ) 1
Example Output: a

Example Input: Problem: a fill pipe can fill 2 / 3 of cistern in 40 minutes in how many minutes , it can fill full of the cistern ? 
Options: a ) 60 min , b ) 36 min , c ) 25 min , d ) 30 min , e ) 50 min
Example Output: a

Example Input: Problem: a boy is travelling from his home to school at 12 km / hr and reached 7 min late . next day he traveled at 16 km / hr and reached 8 min early . distance between home and school ? 
Options: a ) 12 km , b ) 13 km , c ) 14 km , d ) 15 km , e ) 16 km
Example Output:
a