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.

Example Input: Problem: a man can row upstream at 25 kmph and downstream at 55 kmph, and then find the speed of the man in still water ?
Options: a. 65, b. 40, c. 30, d. 78, e. 38
Example Output: b

Example Input: Problem: the circumference of the front wheel of a cart is 30 ft long and that of the back wheel is 32 ft long. what is the distance traveled by the cart, when the front wheel has done five more revolutions than the rear wheel ?
Options: a. 20 ft, b. 25 ft, c. 750 ft, d. 900 ft, e. 2400 ft
Example Output: e

Example Input: Problem: a set s = { x, - 8, - 5, - 1, 1, 6, 9, y } with elements arranged in increasing order. if the median and the mean of the set are the same, what is the value of | x | - | y | ?
Options: a. - 1, b. can not be determined, c. 1, d. 0, e. 2
Example Output:
e