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: 28 buckets of water fill a tank when the capacity of each bucket is 13.5 litres . how many buckets will be required to fill the same tank if the capacity of each bucket is 9 litres ? 
Options: a ) 30 , b ) 42 , c ) 60 , d ) data inadequate , e ) none of these
Example Output: b

Example Input: Problem: a man started driving at a constant speed , from the site of a blast , the moment he heard the blast . he heard a second blast after a time of 30 mins and 25 seconds . if the second blast occurred exactly 30 mins after the first , how many meters was he from the site when he heard the second blast ? ( speed of sound = 330 m / s ) 
Options: a ) 8250 , b ) 9350 , c ) 10,450 , d ) 11,550 , e ) 12,650
Example Output: a

Example Input: Problem: a train 510 m long is running at a speed of 45 km / hr . in what time will it pass a bridge 140 m long ? 
Options: a ) 40 , b ) 52 , c ) 26 , d ) 21 , e ) 14
Example Output:
b