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 sum of all the digits of the integers from 18 to 21 inclusive is 24 ( 1 + 8 + 1 + 9 + 2 + 0 + 2 + 1 = 24 ) . what is the sum t of all the digits of the integers from 0 to 99 inclusive ? 
Options: a ) 450 , b ) 810 , c ) 900 , d ) 1000 , e ) 1100

Ex Output:
c


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: a car was driving at 50 km / h for 30 minutes , and then at 40 km / h for another 30 minutes . what was its average speed ? 
Options: a ) 80 . , b ) 75 . , c ) 70 . , d ) 65 . , e ) 54 .

Ex Output:

a