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 normal price of an article sold at $ 72 after two successive discounts of 10 % and 20 % ?
Options: a. $ 92, b. $ 96, c. $ 100, d. $ 104, e. $ 108
Example Output: c

Example Input: Problem: a can give b 100 meters start and c 200 meters start in a kilometer race. how much start can b give c in a kilometer race ?
Options: a. 111.12 m, b. 221.12 m, c. 271.12 m, d. 611.12 m, e. 191.12 m
Example Output: a

Example Input: Problem: what is the square root of 168,921 ?
Options: a. 476, b. 389, c. 497, d. 411, e. 524
Example Output:
d