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 train 150 m long crosses a platform 130 m long in 20 sec ; find the speed of the train ? 
Options: a ) 50 , b ) 60 , c ) 55 , d ) 45 , e ) 53
Example Output: a

Example Input: Problem: convert 500 miles to km ? 
Options: a ) 600 km , b ) 700 km , c ) 800 km , d ) 900 km , e ) 1000 km
Example Output: c

Example Input: Problem: the sum of four consecutive even numbers is 84 . what would be the largest number ? 
Options: a ) 33 , b ) 88 , c ) 24 , d ) 123 , e ) 12
Example Output:
c