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: when 1 / 20 % of 4,000 is subtracted from 1 / 10 of 4,000 , the difference is 
Options: a ) 50 , b ) 200 , c ) 380 , d ) 398 , e ) 400
Example Output: d

Example Input: Problem: a 20 litre mixture of milk and water contains milk and water in the ratio 3 : 2 . 10 litres of the mixture is removed and replaced with pure milk and the operation is repeated once more . at the end of the two removal and replacement , what is the ratio t of milk and water in the resultant mixture ? 
Options: a ) 17 : 3 , b ) 9 : 1 , c ) 3 : 17 , d ) 5 : 3 , e ) 11 : 2
Example Output: b

Example Input: Problem: in a division , divident is 686 , divisior is 36 and quotient is 19 . find the remainder . 
Options: a ) a ) 4 , b ) b ) 3 , c ) c ) 2 , d ) d ) 5 , e ) e ) 6
Example Output:
c