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: if 8 people take an hour to complete a piece of work , then how long should 16 people will take to complete the same piece of work ? 
Options: a ) 15 min , b ) 30 min , c ) 26 min , d ) 28 min , e ) 18 min
Example Output: b

Example Input: Problem: a train 50 m long takes 6 sec to cross a man walking at 5 kmph in a direction opposite to that of the train . find the speed of the train ? 
Options: a ) 15 kmph , b ) 25 kmph , c ) 35 kmph , d ) 45 kmph , e ) 55 kmph
Example Output: b

Example Input: Problem: on a trip covering 850 km , a bicyclist travels the first 400 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 ) 16.0 , b ) 16.5 , c ) 17.0 , d ) 17.5 , e ) 18.0
Example Output:
c