In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Ex Input:
Problem: a man has some hens and cows . if the number of heads be 60 and the number of feet equals 200 , then the number of hens will be : 
Options: a ) 22 , b ) 25 , c ) 24 , d ) 20 , e ) 28

Ex Output:
d


Ex Input:
Problem: the population of a bacteria culture doubles every 2 minutes . approximately how many minutes will it take for the population to grow from 1,000 to 100,000 bacteria 
Options: a ) 10 , b ) 12 , c ) 14 , d ) 16 , e ) 18

Ex Output:
c


Ex Input:
Problem: a sports equipment store sold ping pong rackets for a total of $ 686 . if the average ( arithmetic mean ) price of a pair of rackets is $ 9.8 , how many pairs were sold ? 
Options: a ) 50 , b ) 100 , c ) 70 , d ) 500 , e ) 980

Ex Output:

c