Ans (A) galaxies
A galaxy is a collection of a vast number of stars and solar systems.
A solar system is a part of a galaxy and is comprised of a sun which is surrounded by various planets, asteroids, comets etc
A planet is again a part of a solar system and essentially orbits the sun.
Moon is a astronomical body which orbits a planet.
For example, planet earth orbiting around the sun is a part of the solar system present in the milky way galaxy.
Ans: The universe is filled with millions of Galaxies grouped in clusters.