7. Sally was trying to create a model that represents the composition of a galaxy. In her model, she needs to distinguish galaxies from other systems of celestial objects. Which of the following best describes the composition of a galaxy?

Dust, gases, billions of stars, and solar systems

Explanation:

A galaxy is a large group of dust, inter stellar gas, stars, solar systems, stellar remnants, dark matter. Some galaxies have over several billions of stars.

Small galaxies are known as dwarfs, which contain a few hundred million stars while large galaxies are known as giants which contain up to a hundred trillion stars

Therefore, the correct option is dust, gases, billions of stars, and solar systems

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