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: today mary ’ s father is 4 times as old as mary . 3 years ago , he was 5 times as old . how old is mary today ? 
Options: a ) 6 , b ) 8 , c ) 10 , d ) 12 , e ) 14
Example Output: d

Example Input: Problem: a train passes a station platform in 31 sec and a man standing on the platform in 20 sec . if the speed of the train is 54 km / hr . what is the length of the platform ? 
Options: a ) 228 , b ) 240 , c ) 165 , d ) 166 , e ) 1811
Example Output: c

Example Input: Problem: what is the ratio of 12 minute to 1 hour ? 
Options: a ) 1 / 4 , b ) 3 / 4 , c ) 1 / 5 , d ) 2 / 2 , e ) 3 / 1
Example Output:
c