Why did the Apollo 11 landing craft and astronauts stay on the surface of the Moon without floating off into outer space?
a. The surface of the Moon exerts static friction, which keeps objects in place.
b. The spring force on the Moon causes any object that springs up to spring back down.
c. The Moon's thin atmosphere provides enough resistance to impede movement.
d. The Moon exerts a gravitational pull that keeps objects on its surface.