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 how many years will a sum of money doubles itself at 12 % per annum on simple interest ? 
Options: a ) 15 % , b ) 20 % , c ) 10 % , d ) 8 % , e ) 22 %
Example Output: d

Example Input: Problem: a $ 500 investment and a $ 1,500 investment have a combined yearly return of 16 percent of the total of the two investments . if the $ 500 investment has a yearly return of 7 percent , what percent yearly return does the $ 1,500 investment have ? 
Options: a ) 9 % , b ) 10 % , c ) 105 / 8 % , d ) 11 % , e ) 19 %
Example Output: e

Example Input: Problem: during a sale , the price of a pair of shoes is marked down 20 % from the regular price . after the sale ends , the price goes back to the original price . what is the percent of increase to the nearest percent from the sale price back to the regular price for the shoes ? 
Options: a ) 9 % , b ) 10 % , c ) 11 % , d ) 15 % , e ) 25 %
Example Output:
e