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: pure milk costs 3.60 per litre . a milkman adds water to 25 litres of pure milk and sells the mixture at 3 per litre . how many litres of water does he add ? 
Options: a ) 2 litres , b ) 5 litres , c ) 7 litres , d ) 11 litres , e ) none of these
Example Output: b

Example Input: Problem: sum of two numbers is 63 . their difference is 1 / 8 of their sum . their l . c . m is 
Options: a ) 231 , b ) 153 , c ) 351 , d ) 345 , e ) 355
Example Output: c

Example Input: Problem: how many odd prime numbers are there less than 100 ? 
Options: a ) 78 , b ) 5 , c ) 24 , d ) 12 , e ) 15
Example Output:
c