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 unit digit in the product ( 784 x 618 x 917 x 463 ) is : 
Options: a ) 5 , b ) 9 , c ) 16 , d ) 2 , e ) 42

Ex Output:
d


Ex Input:
Problem: if a person walks at 20 km / hr instead of 10 km / hr , he would have walked 20 km more . the actual distance traveled by him is : 
Options: a ) 20 km , b ) 56 km , c ) 60 km , d ) 70 km , e ) 80 km

Ex Output:
a


Ex Input:
Problem: if x ^ 2 + ( 1 / x ^ 2 ) = 6 , x ^ 4 + ( 1 / x ^ 4 ) = ? 
Options: a ) 10 , b ) 11 , c ) 12 , d ) 34 , e ) 15

Ex Output:

d