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: 3 different containers contain 496 litres , 403 litres and 713 litres of mixtures of milk and water respectively . what biggest measure can measure all the different quantities exactly ? 
Options: a ) 30 litres , b ) 31 litres , c ) 32 litres , d ) 33 litres , e ) 34 litres
Example Output: b

Example Input: Problem: a zeebra chases a tiger 5 hours after the tiger runs . zeebra takes 6 hours to reach the tiger . if the average speed of the zeebra is 55 kmph , what s the average speed of the tiger ? 
Options: a ) 35 kmph , b ) 32 kmph , c ) 30 kmph , d ) 31 kmph , e ) 20 kmph
Example Output: c

Example Input: Problem: the length of the bridge , which a train 120 meters long and travelling at 45 km / hr can cross in 30 seconds , is ? 
Options: a ) 328 , b ) 279 , c ) 255 , d ) 288 , e ) 211
Example Output:
c