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: if 8 people take an hour to complete a piece of work , then how long should 16 people will take to complete the same piece of work ? 
Options: a ) 15 min , b ) 30 min , c ) 26 min , d ) 28 min , e ) 18 min
Example Output: b

Example Input: Problem: a train passes a station platform in 60 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 ) 615 m , b ) 420 m , c ) 168 m , d ) 197 m , e ) 691 m
Example Output: b

Example Input: Problem: the length of a train and that of a platform are equal . if with a speed of 90 k / hr , the train crosses the platform in one minute , then the length of the train ( in metres ) is : 
Options: a ) 400 , b ) 525 , c ) 750 , d ) 850 , e ) none
Example Output:
c