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.

Ex Input:
Problem: a and b go around a circular track of length 200 m on a cycle at speeds of 36 kmph and 72 kmph. after how much time will they meet for the first time at the starting point ?
Options: a. 120 sec, b. 198 sec, c. 178 sec, d. 20 sec, e. 276 sec

Ex Output:
d

Ex Input:
Problem: a soccer team played 280 games and won 65 percent of them. how many games did it win ?
Options: a. 182, b. 100, c. 104, d. 150, e. 124

Ex Output:
a

Ex Input:
Problem: there is a square with side ' a ' and one octagon is inscribed in it. what will be perimeter of octagon.
Options: ['a. 8 a / 3', 'b. 7 a / 3', 'c. 5 a / 3', 'd. a / 3', 'e. 11 a / 3']

Ex Output:
a