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 prison of 10,000 inmates has enough food to feed them all for 50 days . after 10 days some of the inmates leave and the food is now enough for the same period of 50 days as before . how many of them left ? 
Options: a ) 3,000 , b ) 2,200 , c ) 2,000 , d ) 1,000 , e ) 200
Example Output: c

Example Input: Problem: working alone , pump a can empty a pool in 6 hours . working alone , pump b can empty the same pool in 9 hours . working together , how many minutes will it take pump a and pump b to empty the pool ? 
Options: a ) 192 , b ) 200 , c ) 208 , d ) 216 , e ) 224
Example Output: d

Example Input: Problem: if a can do a work in 10 days and a and b can do a same piece of job in 5 days . in how days can do a work b alone ? 
Options: a ) 10 , b ) 20 , c ) 5 , d ) 15 , e ) 9
Example Output:
a