You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Q: The formation of the Grand Canyon has most likely taken how long?
(A) several years (B) hundreds of years (C) thousands of years (D) millions of years
A:
D