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: dan can do a job alone in 15 hours . annie , working alone , can do the same job in just 10 hours . if dan works alone for 3 hours and then stops , how many hours will it take annie , working alone , to complete the job ? 
Options: a ) 2 , b ) 4 , c ) 6 , d ) 8 , e ) 10
Example Output: d

Example Input: Problem: convert 0.35 in to a vulgar fraction ? 
Options: a ) 18 / 50 , b ) 16 / 50 , c ) 7 / 20 , d ) 19 / 50 , e ) none
Example Output: c

Example Input: Problem: a man travelled from the village to the post - office at the rate of 25 kmph and walked back at the rate of 4 kmph . if the whole journey took 5 hours 48 minutes , find the distance of the post - office from the village 
Options: a ) 20 , b ) 87 , c ) 276 , d ) 198 , e ) 171
Example Output:
a