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: in a certain pond , 80 fish were caught , tagged , and returned to the pond . a few days later , 50 fish were caught again , of which 2 were found to have been tagged . if the percent of tagged fish in the second catch approximates the percent of tagged fish in the pond , what is the approximate number of fish in the pond ? 
Options: a ) 400 , b ) 625 , c ) 1,250 , d ) 2,000 , e ) 10,000
Example Output: d

Example Input: Problem: a man buys an article for $ 10 . and sells it for $ 30 . find the gain percent ? 
Options: a ) 25 % , b ) 50 % , c ) 20 % , d ) 150 % , e ) 300 %
Example Output: e

Example Input: Problem: boy sells a book for rs . 630 he gets a loss of 10 % , to gain 10 % , what should be the sp ? 
Options: a ) 430 , b ) 450 , c ) 550 , d ) 770 , e ) 660
Example Output:
d