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 8000 liter tank , half - full of water is being filled from a pipe with a flow rate of 1 kiloliter every 2 minutes . at the same time , the tank is losing water from two drains at a rate of 1 kiloliter every 4 minutes and every 6 minutes . how many minutes does it take to fill the tank completely ? 
Options: a ) 8 , b ) 12 , c ) 18 , d ) 24 , e ) 48
Example Output: e

Example Input: Problem: rahul travels from a to b a distance of 200 miles in 5 hours . he returns to a in 4 hours . find his average speed ? 
Options: a ) 52.2 mph , b ) 61.9 mph , c ) 44.4 mph , d ) 35.7 mph , e ) 65.6 mph
Example Output: c

Example Input: Problem: a man goes downstream at 12 kmph , and upstream 8 kmph . the speed of the stream is 
Options: a ) 2 kmph , b ) 4 kmph , c ) 16 kmph , d ) 2.5 kmph , e ) 26 kmph
Example Output:
a