I would say excretion since that means the process of expelling waste matter.
When you observe and compare specific physical traits of different birds you will learn that some birds have characteristics that help them live and survive in their own habitat that other birds may not have but make up those birds have characteristics that help them in their own habitat.
What kind of force? There are lots of forces acting on the car at this point.
Will remain at rest or stay in motion. That's Newton's first law of motion
