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: mariah has decided to hire three workers . to determine whom she will hire , she has selected a group of 12 candidates . she plans to have one working interview with 3 of the 12 candidates every day to see how well they work together . how many days will it take her to have working interviews with all the different combinations of job candidates ? 
Options: a ) 720 , b ) 120 , c ) 300 , d ) 30 , e ) 333

Ex Output:
c


Ex Input:
Problem: 20 beavers , working together in a constant pace , can build a dam in 18 hours . how many hours will it take 12 beavers that work at the same pace , to build the same dam ? 
Options: a ) 22 . , b ) 24 . , c ) 30 . , d ) 36 , e ) 38 .

Ex Output:
c


Ex Input:
Problem: a person can row at 10 kmph in still water . if the velocity of the current is 2 kmph and it takes him 15 hour to row to a place and come back , how far is the place ? 
Options: a ) 24 km , b ) 30 km , c ) 48 km , d ) 72 km , e ) 15 km

Ex Output:

d