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 is 20 years older than his son . in two years , his age will be twice the age of his son . the present age of the son is ? 
Options: a ) 11 , b ) 25 , c ) 27 , d ) 18 , e ) 91

Ex Output:
d


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: the average ( arithmetic mean ) of 20 , 40 , and 60 is 5 more than the average of 10 , 50 , and what number ? 
Options: a ) 40 , b ) 45 , c ) 55 , d ) 45 , e ) 50

Ex Output:

d