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: the speed at which a man can row a boat in still water is 16 kmph . if he rows downstream , where the speed of current is 4 kmph , what time will he take to cover 100 metres ? 
Options: a ) 23 , b ) 27 , c ) 28 , d ) 12 , e ) 18
Example Output: e

Example Input: Problem: a tree is 12 m tall and casts an an 8 m long shadow . at the same time , a flag pole caste a 100 m long shadow . how long is the flag pole ? 
Options: a ) 150 m , b ) 200 m , c ) 125 m , d ) 115 m , e ) none
Example Output: a

Example Input: Problem: 35 binders can bind 1400 books in 21 days . how many binders will be required to bind 1600 books in 20 days ? 
Options: a ) 87 , b ) 18 , c ) 42 , d ) 16 , e ) 10
Example Output:
c