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: the overall age of x and y is 19 year greater than the overall age of y and z. z is how many decades younger that x ?
Options: a. 11, b. 15, c. 12, d. 19, e. 20

Ex Output:
d


Ex Input:
Problem: a light flashes every 30 seconds, how many times will it flash in ? of an hour ?
Options: a. 550, b. 600, c. 650, d. 700, e. 120

Ex Output:
e


Ex Input:
Problem: if n is a positive integer and n ^ 2 is divisible by 18, then what is the largest positive integer that must divide n ?
Options: a. 3, b. 4, c. 6, d. 8, e. 9

Ex Output:

c