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: two trains are moving in the same direction at 72 kmph and 36 kmph . the faster train crosses a man in the slower train in 20 seconds . find the length of the faster train ? 
Options: a ) 270 , b ) 277 , c ) 200 , d ) 257 , e ) 271
Example Output: c

Example Input: Problem: a train running at the speed of 54 km / hr crosses a pole in 7 seconds . find the length of the train . 
Options: a ) 150 meter , b ) 105 meter , c ) 140 meter , d ) 135 meter , e ) none of these
Example Output: b

Example Input: Problem: mike 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 500 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 62,500 . 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 ) 13000 , b ) 12500 , c ) 13500 , d ) 14000 , e ) 15000
Example Output:
b