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 man can row 5 kmph in still water . when the river is running at 2 kmph , it takes him 1 hour to row to a place and black . what is the total distance traveled by the man ? 
Options: a ) 5.75 , b ) 5.7 , c ) 5.76 , d ) 4.2 , e ) 5.71
Example Output: d

Example Input: Problem: a and b can do a piece of work in 8 days . with the help of c they finish the work in 4 days . c alone can do that piece of work in ? 
Options: a ) 40 days , b ) 20 days , c ) 8 days , d ) 60 days , e ) 40 days
Example Output: c

Example Input: Problem: a can finish a work in 4 days and b can do same work in half the time taken by a . then working together , what part of same work they can finish in a day ? 
Options: a ) 1 / 4 , b ) 1 / 6 , c ) 1 / 7 , d ) 3 / 4 , e ) none of these
Example Output:
d