Why Does the Moon Have Phases as Observed from Earth

Why does the Moon have phases as observed from Earth?

A) The illuminated half of the Moon becomes more or less visible from Earth as the Moon orbits Earth.
B) The Moon's distance from Earth changes as it moves in its elliptical orbit, thereby changing its apparent brightness.
C) Earth's shadow gradually moves over the Moon's surface as the Moon orbits Earth.
D) The Moon's rotation brings more or less of the illuminated hemisphere into view from Earth.