a moon that orbits a planet a planet that orbits the Sun a very large system of stars that is held together by gravity a very large system of planets that is held together by the Sun
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: What is a galaxy?
Possibilities:
- a moon that orbits a planet
- a planet that orbits the Sun
- a very large system of stars that is held together by gravity
- a very large system of planets that is held together by the Sun

a very large system of stars that is held together by gravity