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 rope of which a calf is tied is increased from 12 m to 23 m, how much additional grassy ground shall it graze ?
Options: a. 2989, b. 2789, c. 1210, d. 1288, e. 1211
Example Output: c

Example Input: Problem: if an investor puts $ 800 in a savings account that earns 10 percent annual interest compounded semiannually, how much money will be in the account after one year ?
Options: a. $ 878, b. $ 880, c. $ 882, d. $ 884, e. $ 886
Example Output: c

Example Input: Problem: a man whose bowling average is 12.4, takes 5 wickets for 26 runs and there by decreases his average by 0.4. the number of wickets taken by him before his last match is ?
Options: a. 82, b. 83, c. 84, d. 85, e. 86
Example Output:
d