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'.

Example Input: Problem: if two of the 4 expressions x + y , x + 5 y , x - y , and 5 x - y are chosen at random , what is the probability w that their product will be of the form of x ^ 2 - ( by ) ^ 2 , where b is an integer ? 
Options: a ) 1 / 2 , b ) 1 / 3 , c ) 1 / 4 , d ) 1 / 5 , e ) w = 1 / 6
Example Output: e

Example Input: Problem: how many even 4 - digit numbers can be formed , so that the numbers are divisible by 4 and no two digits are repeated ? 
Options: a ) 336 , b ) 784 , c ) 1120 , d ) 1804 , e ) 1936
Example Output: c

Example Input: Problem: x is a positive integer less than 500 . when x is divided by 7 , the remainder is 1 ; when x is divided by 3 , the remainder is 2 . how many x are there ? 
Options: a ) 21 , b ) 22 , c ) 23 , d ) 24 , e ) 25
Example Output:
d