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: 6 bells commence tolling together and toll at the intervals of 24 , 68 , 1012 seconds resp . in 60 minutes how many times they will toll together . 
Options: a ) 15 , b ) 16 , c ) 30 , d ) 31 , e ) none of these
Example Output: d

Example Input: Problem: a , b and c completed a piece of work , a worked for 6 days , b for 9 days and c for 4 days . their daily wages were in the ratio of 3 : 4 : 5 . find the daily wages of c , if their total earning was rs . 1702 ? 
Options: a ) s . 109 , b ) s . 115 , c ) s . 100 , d ) s . 103 , e ) s . 102
Example Output: b

Example Input: Problem: david works at a science lab that conducts experiments on bacteria . the population of the bacteria multiplies at a constant rate , and his job is to notate the population of a certain group of bacteria each hour . at 1 p . m . on a certain day , he noted that the population was 600 and then he left the lab . he returned in time to take a reading at 4 p . m . , by which point the population had grown to 4,800 . now he has to fill in the missing data for 2 p . m . and 3 p . m . what was the population at 3 p . m . ? 
Options: a ) 2400 , b ) 3600 , c ) 3000 , d ) 2800 , e ) 2500
Example Output:
a