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: 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: if n is a positive integer and n ^ 2 is divisible by 36, then the largest positive integer that must divide n is
Options: a. 6, b. 12, c. 24, d. 36, e. 48

Ex Output:
a

Ex Input:
Problem: the present population of a town is 1240. population increase rate is 4 % p. a. find the population of town after 1 years ?
Options: a. 990, b. 1215, c. 1345, d. 1142, e. 1290

Ex Output:
e