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: if the sides of a cube are in the ratio 5: 3. what is the ratio of their diagonals ?
Options: ['a. 5: 9', 'b. 9: 3', 'c. 5: 4', 'd. 3: 5', 'e. 5: 3']
Example Output: e

Example Input: Problem: the average weight of a, b and c is 43 kg. if the average weight of a and b be 48 kg and that of b and c be 42 kg, then the weight of b is :
Options: a. 55 kg, b. 53 kg, c. 49 kg, d. 52 kg, e. 51 kg
Example Output: e

Example Input: Problem: a small, rectangular park has a perimeter of 560 feet and a diagonal measurement of 600 feet. what is its area, in square feet ?
Options: ['a. 172,800', 'b. 19,600', 'c. 20,000', 'd. 20,400', 'e. 20,800']
Example Output:
a