Question

which phrase best defines a galaxy?
○ tightly packed group of older stars
○ large grouping of more than two stars
○ loose, disorganized star cluster held together by gravity
○ large collection of stars, gas, and dust held together by gravity

Explanation:

A galaxy is not just a group of stars; it also contains interstellar gas and dust, all bound by gravitational force. The first option describes a globular cluster, the second is too vague (binary/multiple star systems are not galaxies), and the third describes an open cluster, not a galaxy.

Answer:

large collection of stars, gas, and dust held together by gravity