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 train , 800 meter long is running with a speed of 78 km / hr . it crosses a tunnel in 1 minute . what is the length of the tunnel ? 
Options: a ) 650 meter , b ) 555 meter , c ) 500 meter , d ) 458 meter , e ) none of these
Example Output: c

Example Input: Problem: a train 280 m long , running with a speed of 72 km / hr will pass a tree in 
Options: a ) 14 sec , b ) 15 sec , c ) 16 sec , d ) 20 sec , e ) none
Example Output: a

Example Input: Problem: a man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream . the ratio of the speed of the boat ( in still water ) and the stream is : 
Options: a ) 1 : 2 , b ) 2 : 5 , c ) 6 ' ' 2 , d ) 3 : 1 , e ) 4 : 7
Example Output:
d