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'.

Ex Input:
Problem: walking with 5 / 4 of my usual speed , i miss the bus by 5 minutes . what is my usual time ? 
Options: a ) 18 , b ) 19 , c ) 20 , d ) 22 , e ) 24

Ex Output:
c


Ex Input:
Problem: a river boat leaves silver town and travels upstream to gold town at an average speed of 6 kilometers per hour . it returns by the same route at an average speed of 5 kilometers per hour . what is the average speed for the round - trip in kilometers per hour ? 
Options: a ) 5.5 , b ) 7.1 , c ) 7.2 , d ) 7.0 , e ) 8.0

Ex Output:
a


Ex Input:
Problem: a is half good a work man as b and together they finish a job in 15 days . in how many days working alone b finish the job ? 
Options: a ) 23 , b ) 22 , c ) 45 / 2 , d ) 36 , e ) 48

Ex Output:

c