Question

When two stars are bound together gravitationally and orbit a common mass, they're known as
A. meteoroids.
B. galaxies.
C. constellations.
D. binary stars.

Answer 1

D. Binary Stars

Well, galaxies are not stars at all rather they are collection of stars, nebulae, globular clusters and stuff like this.
Meteoroids are something entirely different.
Constellations are the pattern of stars.
So, "Binary Stars" is the Right One.