Why Do We See Different Phases of the Moon

Why do we see different phases of the Moon?

A) The motion of the Moon in its orbit around Earth causes us to see different amounts of Earth's shadow falling on the Moon.
B) The motion of the Moon in its orbit around Earth causes us to see different amounts of the sunlit side of the Moon.
C) The distance of the Moon from Earth changes because of the elliptical orbit of the Moon, causing the sunlit side of the Moon to move relative to Earth.
D) The rotation of the Moon around its own axis causes us to see different amounts of the sunlit side of the Moon.