A rock rests on the ground. A force pulls the rock toward the earth, and another force pulls the rock toward the moon. Why does the rock stay on the ground?

A. The force pulling the rock toward the earth is weaker than the force pulling the rock toward the moon.

B. The rock is moving, but it's not visible to the human eye.

C. Only one force can act on an object at one time.

D. The force pulling the rock toward the earth is greater than the force pulling the rock toward the moon.