Which of the following describes a role of gravity in the formation of our solar system?

I. In the early stages of solar system formation, a fragment of an interstellar cloud of dust and gas collapsed and began rotating under the influence of gravity.
II. The eight planets were originally orbiting a nearby star, and the Sun's gravity pulled those planets into orbit around the Sun.
III. Gravity caused small particles in the rotating solar nebula to stick together and form larger particles. This process repeated itself, forming larger and larger particles that eventually became planets.
IV. The combined gravities of the planets pulled the Sun away from a nearby star cluster and into the center of the solar system.