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: the length of the bridge , which a train 140 metres long and travelling at 45 km / hr can cross in 30 seconds , is : 
Options: a ) 200 m , b ) 235 m , c ) 245 m , d ) 250 m , e ) 270 m
Example Output: b

Example Input: Problem: a train passes a station platform in 20 sec and a man standing on the platform in 12 sec . if the speed of the train is 72 km / hr . what is the length of the platform ? 
Options: a ) 227 , b ) 140 , c ) 160 , d ) 120 , e ) 171
Example Output: c

Example Input: Problem: a and b can do a piece of work in 10 days , b and c in 15 days , c and a in 12 days . how long will c take to do it ? 
Options: a ) 70 days , b ) 55 days , c ) 24 days , d ) 40 days , e ) 11 days
Example Output:
d