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 gets 40 kilometers per gallon of gasoline . how many gallons of gasoline would the car need to travel 210 kilometers ? 
Options: a ) 8.25 gallons , b ) 7.5 gallons , c ) 6.55 gallons , d ) 5.25 gallons , e ) 4.5 gallons
Example Output: d

Example 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
Example Output: c

Example Input: Problem: if two - third of a bucket is filled in 90 seconds then the time taken to fill the bucket completely will be . 
Options: a ) 90 seconds , b ) 70 seconds , c ) 135 seconds , d ) 100 seconds , e ) 120 seconds
Example Output:
c