Final answer:
The normal force is the force that a surface applies to an object to support its weight and keep it stationary.
Step-by-step explanation:
The answer to the question is D. Normal force.
When an object remains stationary, there are forces acting on it. One of these forces is the normal force. The normal force is the force that a surface applies to an object to support its weight. It acts perpendicular to the surface upon which the object rests.
For example, when an object is placed on a table, the table exerts a normal force on the object to support its weight and keep it stationary.