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: two trains 180 m and 160 m long run at the speed of 60 km / hr and 40 km / hr respectively in opposite directions on parallel tracks . the time which they take to cross each other is ?
Options: a ) 10.7 , b ) 10.9 , c ) 10.24 , d ) 12.24 , e ) 18.8
Example Output: d

Example Input: Problem: the distance between a & b is 600 km . a person is traveling from a to b at 70 km / hr started at 10 am and another person is traveling from b to a at 80 km / hr and started at same time . then at what time they meet together .
Options: a ) 2 pm , b ) 4 pm , c ) 1 pm , d ) 3 pm , e ) 5 pm
Example Output: a

Example Input: Problem: a swimmer can swim in still water at 4 km / h . if the speed of the water current is 1 km / h , how many hours will the swimmer take to swim against the current for 6 km ?
Options: a ) 1.2 , b ) 1.4 , c ) 1.6 , d ) 1.8 , e ) 2
Example Output:
e