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: what is the probability of getting a queen or spade from a set of cards ?
Options: a. 3 / 13, b. 4 / 13, c. 5 / 13, d. 6 / 13, e. 7 / 13

Ex Output:
b


Ex Input:
Problem: if 7 a = 8 b and ab ≠ 0, what is the ratio of a / 8 to b / 7 ?
Options: a. 16 / 14, b. 8 / 7, c. 1, d. 7 / 8, e. 64 / 49

Ex Output:
c


Ex Input:
Problem: how many integers v are prime numbers in the range 200 < v < 220 ?
Options: a. 1, b. 2, c. 3, d. 4, e. 5

Ex Output:

a