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'.

Ex Input:
Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 5 days , then the fraction of the work that is left is : 
Options: a ) 1 / 3 , b ) 7 / 12 , c ) 5 / 12 , d ) 2 / 3 , e ) 1 / 2

Ex Output:
c


Ex Input:
Problem: two trains are moving in the same direction at 72 kmph and 36 kmph . the faster train crosses a man in the slower train in 20 seconds . find the length of the faster train ? 
Options: a ) 270 , b ) 277 , c ) 200 , d ) 257 , e ) 271

Ex Output:
c


Ex Input:
Problem: at a time a , do 20 % less work than b . if a do any work in 15 / 2 hour , then in how many hour b will finish work ? 
Options: a ) 5 hour , b ) 11 / 2 hour , c ) 6 hour , d ) 13 / 2 hour , e ) 8 hour

Ex Output:

c