An empty office chair is at rest on a floor. Consider the following forces:
1. A downward force of gravity.
2. An upward force exerted by the floor.
3. A net downward force exerted by the air.
Which of the forces is (are) acting on the office chair?
(A) 1 only.
(B) 1 and 2.
(C) 2 and 3.
(D) 1, 2, and 3.
(E) none of the forces. (Since the chair is at rest there are no forces acting upon it.)