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: a train overtakes two person who are walking in the same direction in which the train is going , at the rate of 2 kmph and 4 kmph and passes them completely in 9 and 10 seconds respectively . the length of the train is : 
Options: a ) 45 m , b ) 50 m , c ) 54 m , d ) 72 m , e ) none of these
Example Output: b

Example Input: Problem: some persons can do a piece of work in 12 days . two times the number of these people will do half of that work in ? 
Options: a ) 3 , b ) 4 , c ) 5 , d ) 6 , e ) 8
Example Output: a

Example Input: Problem: how many bricks each measuring 30 cm x 12 cm x 10 cm , will be needed to build a wall 6 m x 4 m x 20.5 m 
Options: a ) 5655 , b ) 1366 , c ) 6444 , d ) 7266 , e ) none of these
Example Output:
b