Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.

[Q]: Problem: two trains travel in opposite directions at 36 kmph and 45 kmph and a man sitting in slower train passes the faster train in 8 seconds. the length of the faster train is
Options: a. 80 m, b. 100 m, c. 120 m, d. 180 m, e. 160 m
[A]: b


[Q]: Problem: if s is the sum of reciprocals of a list of consecutive integers from 55 to 64, inclusive, s is approximately equal to
Options: a. 0.16, b. 0.2, c. 0.3, d. 0.4, e. 0.5
[A]: a


[Q]: Problem: a swimmer can swim in still water at 4 km / h. if the speed of the water current is 2 km / h, how many hours will the swimmer take to swim against the current for 5 km ?
Options: a. 2.0, b. 2.5, c. 3.0, d. 3.5, e. 4.0
[A]:
b