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 70 cm long wire is to be cut into two pieces so that one piece will be 2 / 3 th of the other , how many centimeters will the shorter piece be ? 
Options: a ) 35 , b ) 20 , c ) 28 , d ) 36 , e ) 30
Example Output: c

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 train 640 m in length crosses a telegraph post in 16 seconds . the speed of the train is ? 
Options: a ) 22 kmph , b ) 77 kmph , c ) 144 kmph , d ) 71 kmph , e ) 88 kmph
Example Output:
c