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 man can do a piece of work in 4 days , but with the help of his son he can do it in 3 days . in what time can the son do it alone ? 
Options: a ) 12 days , b ) 6 days , c ) 5 days , d ) 4 days , e ) none of these
Example Output: a

Example Input: Problem: a can finish a work in 20 days , b in 15 days and c in 12 days . b and c start the work but are forced to leave after 2 days . the remaining work was done by a in : 
Options: a ) 10 , b ) 11 , c ) 12 , d ) 13 , e ) 14
Example Output: e

Example Input: Problem: excluding stoppages , the speed of a train is 45 kmph and including stoppages it is 31 kmph . of how many minutes does the train stop per hour ? 
Options: a ) 18.6 , b ) 27 , c ) 12 , d ) 121 , e ) 28
Example Output:
a