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: due to construction , the speed limit along an 5 - mile section of highway is reduced from 60 miles per hour to 40 miles per hour . approximately how many minutes more will it take to travel along this section of highway at the new speed limit than it would have taken at the old speed limit ? 
Options: a ) a ) 3.12 , b ) b ) 2.5 , c ) c ) 10 , d ) d ) 15 , e ) e ) 24
Example Output: b

Example Input: Problem: the population of a bacteria colony doubles every day . if it was started 8 days ago with 3 bacteria and each bacteria lives for 12 days , how large is the colony today ? 
Options: a ) 512 , b ) 768 , c ) 13122 , d ) 2048 , e ) 4096
Example Output: c

Example Input: Problem: a train covers a distance of 12 km in 16 min . if it takes 6 sec to pass a telegraph post , then the length of the train is ? 
Options: a ) 80 , b ) 90 , c ) 60 , d ) 75 , e ) 85
Example Output:
d