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: there is one 4 - digit whole number n, such that the last 4 digits of n 2 are in fact the original number n
Options: a. 8476, b. 7376, c. 9376, d. 7378, e. 9466
c