Given the task definition and input, reply with output. 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.

Problem: the sum of the even numbers between 1 and n is 89 * 90, where n is an odd number, then n = ?
Options: a. 167, b. 173, c. 179, d. 185, e. 193
c