Why Does the Moon Show Phases in the Course of a Month

Multiple Choice

Why does the Moon show phases in the course of a month?

A) clouds get in the way of the Moon's light and cover up parts of it
B) the Earth's shadow falls on the Moon to different degrees as the Moon goes around
C) the angle the Moon makes with the Sun changes and we see differing amounts of reflected sunlight
D) more or less light from the Earth is reflected as the Moon turns around it
E) the Moon glows from the inside, and its various continents glow different amounts