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: how much more would rs. 10000 fetch, after two years, if it is put at 20 % p. a. compound interest payable half yearly than if is put at 20 % p. a. compound interest payable yearly ?
Options: a. 241, b. 725, c. 992, d. 837, e. 923
Example Output: a

Example Input: Problem: the area of a square field is 625 km 2. how long will it take for a horse to run around at the speed of 25 km / h ?
Options: a. 12 h, b. 10 h, c. 8 h, d. 4 h, e. none of these
Example Output: d

Example Input: Problem: 5005 - 5000 ÷ 10.00 = ?
Options: a. 0.5, b. 50, c. 5000, d. 4505, e. none
Example Output:
d