Answer:
C. Gravity
Step-by-step explanation:
Gravity is the force that attracts objects with mass toward each other. It is the force that keeps all of the stars, planets, and other objects in a galaxy together.
Dark matter and dark energy may play a role in the formation and evolution of galaxies, but they are not the primary force that holds galaxies together. Redshift is a type of phenomenon that occurs when light is shifted to longer wavelengths due to the expansion of the universe.