An elevator is rising up a vertical shaft in a skyscraper. Between the 12th and 20th floors, it travels at a constant speed. During this time period:
1.) The only unbalanced force acting on it is air resistance.
2.) The forces acting on it are balanced so the net force is zero.
3.) The upward force is greater than the combined downward forces of gravity and air resistance, making it move upward.
4.) There are no forces acting on it so the net force is zero.