Answer:
At Segment A, the elevator is going up so the rate of change is positive. The incline of the line explains that there is constant velocity.
At Segment B, the elevator is standing still so the rate of change is 0. There is no incline or decline of the line (flat) which explains that the elevator is not moving.
At Segment C, the elevator is going up so the rate of change is negative. The decline of the line explains that the elevator is going down at a constant speed.