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: 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: a cistern is normally filled in 10 hrs , but takes 2 hrs longer to fill because of a leak on its bottom , if cistern is full , how much time citern would empty ? 
Options: a ) 10 hours , b ) 20 hours , c ) 60 hours , d ) 40 hours , e ) 50 hours
Example Output: c

Example Input: Problem: a man traveled a total distance of 1800 km . he traveled one - third of the whole trip by plane and the distance traveled by train is three - fifth of the distance traveled by bus . if he traveled by train , plane and bus , then find the distance traveled by bus ? 
Options: a ) 239 , b ) 247 , c ) 277 , d ) 270 , e ) 898
Example Output:
d