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: there are two tanks a & b with same capacity of 20 litres . if the water inflow rate ( speed ) in tank a is 2 litres per hour & in tank b is 4 litres per hour . how much longer tank a takes to fill than tank b ? 
Options: a ) 4 hours , b ) 5 hours , c ) 3 hours , d ) 2 hours , e ) 1 hour
Example Output: b

Example Input: Problem: ajay can walk 6 km in 1 hour . in how many hours he can walk 70 km ? 
Options: a ) 5 hrs , b ) 11.6 hrs , c ) 15.6 hrs , d ) 20.1 hrs , e ) 30 hrs
Example Output: b

Example Input: Problem: 3 pumps , working 8 hours a day , can empty a tank in 2 days . how many hours a day must 15 pumps work to empty the tank in 1 day ? 
Options: a ) 3.5 , b ) 4.8 , c ) 5.1 , d ) 5.2 , e ) 6.3
Example Output:
a