Planets move along elliptical orbits because planets move in a gravitational force field which falls off as one over the square of the distance between the sun and the planet ( Force = GMm/r^2 from Newton's Law of Gravity).
(planets; move; in a gravitational force field) (a gravitational force field; falls; off; as one over the square of the distance between the sun and the planet)
planets a gravitational force field
move falls
in a gravitational force field
off as one over the square of the distance between the sun and the planet