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: how many liters of a 40 % iodine solution need to be mixed with 35 liters of a 20 % iodine solution to create a 32 % iodine solution ? 
Options: a ) 35 , b ) 49 , c ) 100 , d ) 102 , e ) 140
Example Output: d

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 sells an article at a profit of 25 % . if he had bought it at 20 % less and sold it for rs . 14.70 less , he would have gained 30 % . find the cost of the article . 
Options: a ) 30 , b ) 40 , c ) 50 , d ) 60 , e ) 70
Example Output:
e