Teacher: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").
Teacher: Now, understand the problem? Solve this instance: the phases of the moon change the appearance of what? (A) mars (B) astral night light (C) earth (D) sun
Student:

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
B