In this task, you need to answer the given multiple-choice question on the gain. Gain is the value by which to multiply the input. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: if each year the population of the country grows by 40 % , how many years will elapse before the population of the country doubles ? 
Options: a ) 3 , b ) 4 , c ) 5 , d ) 6 , e ) 7
Example Output: a

Example Input: Problem: what is 120 % of 13 / 24 of 840 ? 
Options: a ) 436 , b ) 478 , c ) 512 , d ) 546 , e ) 620
Example Output: d

Example Input: Problem: on selling 17 balls at rs . 720 , there is a loss equal to the cost price of 5 balls . the cost price of a ball is : 
Options: a ) rs . 20 , b ) rs . 60 . , c ) rs . 40 , d ) rs . 30 , e ) rs . 90
Example Output:
b