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 bag contains 21 toys numbered 1 to 21. a toy is drawn and then another toy is drawn without replacement. find the probability that both toys will show even numbers.
Options: a. 5 / 21, b. 9 / 42, c. 6 / 22, d. 4 / 21, e. 3 / 21

Ex Output:
b


Ex Input:
Problem: the total age of a and b is 16 years more than the total age of b and c. c is how many year younger than
Options: a. 14 years, b. 12 years, c. 56 years, d. 16 years, e. 55 years

Ex Output:
d


Ex Input:
Problem: he ratio between the sale price and the cost price of an article is 5: 6. what is the ratio between the profit and the cost price of that article ?
Options: a. 2: 6, b. 1: 8, c. 1: 6, d. 2: 1, e. 2: 5

Ex Output:

c