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: a man can row upstream at 15 kmph and downstream at 25 kmph , and then find the speed of the man in still water ? 
Options: a ) 27 , b ) 29 , c ) 30 , d ) 20 , e ) 24
Example Output: d

Example Input: Problem: how many seconds will a train 100 meters long take to cross a bridge 160 meters long if the speed of the train is 36 kmph ? 
Options: a ) 26 , b ) 72 , c ) 25 , d ) 82 , e ) 27
Example Output: a

Example Input: Problem: if the perimeter of a rectangular park is 1000 m , its length when its breadth is 200 m is ? 
Options: a ) 50 , b ) 100 , c ) 200 , d ) 300 , e ) 400
Example Output:
d