During its early stages of formation, a catastrophic collision with Earth by a large body is thought to have ripped part of the Earth away to form:

A) the Moon
B) asteroid belt
C) Mars
D) Phobos and Deimos

The prevailing theory, known as the giant-impact hypothesis, suggests that the Moon formed from the debris left over after a collision between Earth and a Mars-sized body, often referred to as Theia, early in the Solar System's history.