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 a : b = 2 : 3 , b : c = 4 : 5 and c : d = 5 : 9 then a : d is equal to : 
Options: a ) 11 : 17 , b ) 8 : 27 , c ) 5 : 9 , d ) 2 : 9 , e ) none
Example Output: b

Example Input: Problem: the average of the marks of 30 students in a class is 45 . if the marks of each student are doubled , find the new average ? 
Options: a ) 85 , b ) 77 , c ) 33 , d ) 90 , e ) 75
Example Output: d

Example Input: Problem: if x is the sum of first 100 positive even integers and y is the sum of first 100 positive odd integers , what is the value of x - y ? please try to explain your answers 
Options: a ) 0 , b ) 25 , c ) 50 , d ) 75 , e ) 100
Example Output:
e