In this task, you need to answer the given multiple-choice question on the physics. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Example Input: Problem: on a trip covering 400 km , a bicyclist travels the first 100 km at 20 km per hour and the remainder of the distance at 15 km per hour . what is the average speed , in km per hour , for the entire trip ? 
Options: a ) 15.5 , b ) 16.0 , c ) 16.5 , d ) 17.0 , e ) 17.5
Example Output: b

Example Input: Problem: 28 buckets of water fill a tank when the capacity of each bucket is 13.5 litres . how many buckets will be required to fill the same tank if the capacity of each bucket is 9 litres ? 
Options: a ) 30 , b ) 42 , c ) 60 , d ) data inadequate , e ) none of these
Example Output: b

Example Input: Problem: the h . c . f . of two numbers is 12 and their l . c . m . is 520 . if one of the numbers is 480 , then the other is : 
Options: a ) 13 , b ) 18 , c ) 21 , d ) 24 , e ) 38
Example Output:
a