What causes the Moon’s phases?

A: The Sun lights up only one half of the Moon and as the Sun orbits the Earth we can sometimes see the unlit side of the Moon.

B: The Sun lights up only one half of the Moon and as the Moon orbits the Earth we can sometimes see the unlit side of the Moon.

C: The Earth's shadow falls on the Moon, blocking the sunlight.

D: The Moon's shadow falls on the Earth, blocking the sunlight.