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: 8 persons can build a wall 140 m long in 42 days . in how many days can 30 persons complete a similar wall 100 m long ? 
Options: a ) 12 , b ) 10 , c ) 8 , d ) 6 , e ) 5
Example Output: c

Example Input: Problem: how many paying stones , each measuring 2 m * 2 m are required to pave a rectangular court yard 30 m long and 18 m board ? 
Options: a ) 99 , b ) 18 , c ) 135 , d ) 17 , e ) 12
Example Output: c

Example Input: Problem: a train speeds past a pole in 15 sec and a platform 100 m long in 25 sec , its length is ? 
Options: a ) 158 m , b ) 150 m , c ) 110 m , d ) 130 m , e ) 157 m
Example Output:
b