Which of the following situations is an example of an unbalanced force acting on an object?

• A. A tug-of-war ends in a tie with equal pulls on both sides of the rope.
• B. A book rests on a table with gravity downward and the normal force upward of equal magnitude.
• C. A skydiver falls at terminal velocity with air resistance equal in magnitude to weight.
• D. A car accelerates forward because the forward static friction force from the road is greater than the backward resistive forces.

Answer: (D)