Which statement best describes what keeps galaxies together?

A. The stars and other bodies of a galaxy are held together because of their
motion and the gravitational pull toward the outer regions of the
galaxy.

B. The stars and other bodies of a galaxy are held together because of mutual
gravitational attraction to one another and the gravitational pull toward
matter in the center of the galaxy.

C. The stars and other bodies of a galaxy are held together because of their
small size and the gravitational pull of other galaxies.

D. The stars and other bodies of a galaxy are held together because of the
gravitational pull of our sun and the gravitational pull of the outer regions of
the galaxy.