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: 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 man can row 4 kmph in still water . when the river is running at 1.8 kmph , it takes him 1 hour to row to a place and black . what is the total distance traveled by the man ?
Options: a ) 7.13 , b ) 6.19 , c ) 4.12 , d ) 3.19 , e ) 4.21
Example Output: b

Example Input: Problem: a can do a job in 18 days and b can do it in 30 days . a and b working together will finish twice the amount of work in days ?
Options: a ) 29 days , b ) 22 days , c ) 92 days , d ) 28 days , e ) 92 days
Example Output:
b