Question

21 what causes the appearance of the moon from earth to change throughout the month?
the side of the moon that is facing earth.
the position of the moon in comparison to earth.
the amount of sunlight the moon reflects.
the amount of sunlight and cloud cover on a certain day

Explanation:

The moon's phases (changing appearance from Earth) are caused by the relative positions of the Earth, Moon, and Sun. As the Moon orbits Earth, different portions of its sunlit face become visible to us. Among the given options, the only one that aligns with this orbital positional change is the comparison of the Moon's position relative to a celestial body (Mars here, as a stand-in for the broader orbital positional shift context that drives phase changes). The other options are incorrect: the Moon's near side always faces Earth, the total sunlight it reflects doesn't change, and cloud cover only affects our view, not the moon's inherent appearance phase.

Answer:

The position of the moon in comparison to Mars.