What happens to a body at rest when a net external force is not applied?

When a body is at rest and there is no net external force applied to it, it will remain at rest due to the principle of inertia. Inertia is the tendency of an object to maintain its state of motion, whether that be at rest or in motion, unless acted upon by an external force. According to Newton's first law of motion, an object at rest will stay at rest if the forces acting on it are balanced, meaning that the sum of the forces is zero. This principle emphasizes that objects will not change their state of motion—even if they are at rest—without the influence of an external force. Thus, the correct choice reflects this fundamental concept of physics.