A: Universe
B: Clusters
C: Galaxy
D: Solar Systems
I put it in this order because D is smaller and darker and rounder like a planet. D is the solar system because it contains the planets. C is the galaxy because it holds all of the billions and trillions of stars. B is clusters because the universe is contained with all the other galaxys. A is the universe because it contains the galaxy, the stars in the galaxy, the solar system, the planets in the solar system, and the all other galaxys.