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: 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: two trains are moving in the same direction at 72 kmph and 36 kmph . the faster train crosses a man in the slower train in 20 seconds . find the length of the faster train ?
Options: a ) 270 , b ) 277 , c ) 200 , d ) 257 , e ) 271
Example Output: c

Example Input: Problem: a can do a piece of work in 10 days . he works at it for 4 days and then b finishes it in 9 days . in how many days can a and b together finish the work ?
Options: a ) 6 , b ) 7 , c ) 5 , d ) 4 , e ) 1
Example Output:
a