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.

Example Input: Problem: the average of first five multiples of 7 is :
Options: a. 9, b. 16, c. 15, d. 8, e. 21
Example Output: e

Example Input: Problem: the average age of 15 students of a class is 15 years. out of these, the average age of 8 students is 14 years and that of the other 6 students is 16 years, the age of the 15 th student is
Options: a. 17, b. 12, c. 13, d. 14, e. 15
Example Output: a

Example Input: Problem: 3 / 5 of all married couples have more than one child. 1 / 4 of all married couples have more than 3 children. what fraction of all married couples have 2 or 3 children ?
Options: a. 1 / 5, b. b. 1 / 4, c. 7 / 20, d. 3 / 5, e. it can not be determined from the given information.
Example Output:
c