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 , b and c can complete a piece of work in 24 , 6 and 12 days respectively . working together , they will complete the same work in :
Options: a ) 33 / 7 , b ) 43 / 7 , c ) 24 / 7 , d ) 19 / 7 , e ) none
Example Output: c

Example Input: Problem: the speed of a car is 60 km in the first hour and 30 km in the second hour . what is the average speed of the car ?
Options: a ) 45 kmph , b ) 65 kmph , c ) 75 kmph , d ) 85 kmph , e ) 90 kmph
Example Output: a

Example Input: Problem: a person crosses a 720 m long street in 12 minutes . what is his speed in km per hour ?
Options: a ) 3.6 , b ) 4.5 , c ) 4.8 , d ) 5.4 , e ) 5.5
Example Output:
a