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: what is the perimeter of a square field whose diagonal is 8 â ˆ š 2 ?
Options: a. 64 m, b. 32 m, c. 30 m, d. 16 m, e. 18 m
Example Output: b

Example Input: Problem: buses a and b start from a common bus stop x. bus a begins to travel in a straight line away from bus b at a constant rate of 30 miles per hour. one hour later, bus b begins to travel in a straight line in the exact opposite direction at a constant rate of 50 miles per hour. if both buses travel indefinitely, what is the positive difference, in minutes, between the amount of time it takes bus b to cover the exact distance that bus a has covered and the amount of time it takes bus b to cover twice the distance that bus a has covered ?
Options: a. 36, b. 84, c. 132, d. 144, e. 180
Example Output: b

Example Input: Problem: if a ' s height is 40 % less than that of b, how much percent b ' s height is more than that of a ?
Options: a. 66.66 %, b. 66.68 %, c. 66.766 %, d. 86.66 %, e. 66.65 %
Example Output:
a