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: annika hikes at a constant rate of 12 minutes per kilometer . she has hiked 2.75 kilometers east from the start of a hiking trail when she realizes that she has to be back at the start of the trail in 40 minutes . if annika continues east , then turns around and retraces her path to reach the start of the trail in exactly 40 minutes , for how many kilometers total did she hike east ? 
Options: a ) 3.625 , b ) 3.5 , c ) 3 , d ) 3.04 , e ) 4
Example Output: d

Example Input: Problem: a train running at a speed of 60 kmph crosses a pole in 18 seconds . what is the length of the train ? 
Options: a ) 120 m , b ) 300 m , c ) 190 m , d ) 150 m , e ) 160 m
Example Output: b

Example Input: Problem: the current in a river is 10 mph . a boat can travel 50 mph in still water . how far up the river can the boat travel if the round trip is to take 5 hours ? 
Options: a ) 120 , b ) 100 , c ) 96 , d ) 85 , e ) 150
Example Output:
a