The sum of all forces that act upon an object Reaction force
Net force
Unbalanced force
Balanced force

B) Net force

Think of each force as a push or pull on the object. For example, the force of gravity pulls down on an object, while the ground pushes back up to prevent the object from falling through the ground. This force pushing back up is known as the normal force.

When you are asking for the expression to be in the simplest form, that means there is no one term that is collected into a like term. meaning that a would be your answer to that as all of the terms have different variables that cannot be collected into like terms.