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: at the end of the month , a certain ocean desalination plant ’ s reservoir contained 14 million gallons of water . this amount is twice the normal level . if this amount represents 70 % of the reservoir ’ s total capacity , how many million gallons short of total capacity is the normal level ? 
Options: a ) 2 , b ) 5 , c ) 10 , d ) 12 , e ) 15
Example Output: c

Example Input: Problem: if 3 x – 5 y = 5 and x / x + y = 5 / 7 , then what is the value of x – y ? 
Options: a ) 9 , b ) 6 , c ) 4 , d ) 3 , e ) none of these
Example Output: d

Example Input: Problem: how many times digit 20 is used while writing numbers from 100 to 500 ? 
Options: a ) 20 , b ) 30 , c ) 15 , d ) 25 , e ) 20
Example Output:
a