The correct answer is C. Gravity and inertia.
Step-by-step explanation
Gravity is a force that makes objects attract other objects. Earth, planets, sun, moon, and other objects in the universe have forces of gravity that allow them to be in a constant orbit. For example, the sun's gravity makes the planets of the solar system rotate around it, however, not only does the force of gravity act. The other factor that influences this movement is the law of inertia that establishes that an object is going to remain in constant rest or movement with constant speed as long as an external force does not act on it. Therefore, it is possible to affirm that what allows the Earth to orbit around the Sun and the moon around the Earth, is the force of gravity and the law of inertia. So, the correct answer is C. Gravity and inertia.