Question

What role did gravity play in the formation of the planets?

Answer 1

Gravitational forces brought together several moon-sized bodies, called planetesimals, to form larger bodies that became planets.

Answer 2

Your answer would be D.
If an object has mass, it has gravity, and the more mass it has, the stronger its gravity. During the formation of planets, essentially, various matter and elements pulled and fused together (because of the gravity), forming planetesimals.