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 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: if 21 lines are drawn in a plane such that no two of them are parallel and no three are concurrent , then in how many points do they intersect ? 
Options: a ) 150 , b ) 170 , c ) 190 , d ) 210 , e ) 230
Example Output: d

Example Input: Problem: there are 28 stations between ernakulam and chennai . how many second class tickets have to be printed , so that a passenger can travel from one station to any other station ? 
Options: a ) 800 , b ) 820 , c ) 850 , d ) 870 , e ) 900
Example Output:
d