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 can give b 50 meters start and c 100 meters start in a kilometer race. how much start can b give c in a kilometer race ?
Options: a. 111.12, b. 111.67, c. 111.64, d. 52.63, e. 101.12
Example Output: d

Example Input: Problem: the ratio of the volumes of two cubes is 1331: 2197. what is the ratio of their total surface areas ?
Options: a. 121: 169, b. 169: 122, c. 81: 124, d. 81: 126, e. 81: 129
Example Output: a

Example Input: Problem: two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. the ratio of their speeds i
Options: a. 1: 3, b. 3: 2, c. 3: 4, d. 4: 2, e. none of these
Example Output:
b