In this task, you are given a multiple-choice question and you have to pick the correct option. Answer with option indexes (i.e., "A", "B", "C", and "D").

the Grand Canyon was formed by the Colorado River doing what over long periods of time? (A) blazing (B) melting (C) moving steadily (D) evaporating

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
C