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: when the perimeter of a regular polygon is divided by 5 , the length of a side is 25 . what is the name of the polygon ? what is the perimeter ? 
Options: ['a ) 125', 'b ) 126', 'c ) 127', 'd ) 128', 'e ) 129']
Example Output: a

Example Input: Problem: two cyclist start on a circular track from a given point but in opposite direction with speeds of 7 m / s and 8 m / s . if the circumference of the circle is 630 meters , after what time will they meet at the starting point ? 
Options: a ) 20 sec , b ) 15 sec , c ) 42 sec , d ) 50 sec , e ) 1 min
Example Output: c

Example Input: Problem: a train consists of 12 boggies , each boggy 15 metres long . the train crosses a telegraph post in 18 seconds . due to some problem , three boggies were detached . the train now crosses a telegraph post in 
Options: a ) 18 sec , b ) 12 sec , c ) 15 sec , d ) 20 sec , e ) 13.5 sec
Example Output:
e