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: 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 cyclist rides a bicycle 7 km at an average speed of 10 km / hr and again travels 10 km at an average speed of 7 km / hr . what is the average speed for the entire trip ?
Options: a ) 7.59 , b ) 7.79 , c ) 7.99 , d ) 8.19 , e ) 8.39

Ex Output:
c

Ex Input:
Problem: dan ' s age after 16 years will be 4 times his age 8 years ago . what is the present age of dan ?
Options: a ) 12 , b ) 16 , c ) 20 , d ) 24 , e ) 28

Ex Output:
b