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 the sides of a cube are in the ratio 5: 3. what is the ratio of their diagonals ?
Options: ['a. 5: 9', 'b. 9: 3', 'c. 5: 4', 'd. 3: 5', 'e. 5: 3']

Ex Output:
e

Ex Input:
Problem: if the population of a certain country increases at the rate of one person every 15 seconds, by how many persons does the population increase in 25 minutes ?
Options: a. 80, b. 100, c. 150, d. 240, e. 300

Ex Output:
b

Ex Input:
Problem: a number when divided by 5, gives 45 as quotient and 0 as remainder. what will be the remainder when dividing the same number by 10
Options: a. a. 5, b. b. 3, c. c. 4, d. d. 6, e. e. 7

Ex Output:
a