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 car runs at the speed of 25 km per hour when not serviced and runs at 75 kmph when serviced . after servicing the car covers a certain distance in 5 hours . how much time will the car take to cover the same distance when not serviced ? 
Options: a ) 8 hours , b ) 16 hours , c ) 15 hours , d ) 7 hours , e ) none
Example Output: d

Example Input: Problem: a man can row a boat at 10 kmph in still water and the speed of the stream is 8 kmph . what is then time taken to row a distance of 90 km down the stream ? 
Options: a ) 8 hrs , b ) 5 hrs , c ) 15 hrs , d ) 15 hrs , e ) 20 hrs
Example Output: b

Example Input: Problem: a is 30 % more efficient than b . how much time they will working together take to complete a job which a alone could have done in 23 days ? 
Options: a ) 25 days , b ) 13 days , c ) 14 days , d ) 20 days , e ) 15 days
Example Output:
b