A "Galactic Year" as Defined by Astronomers Is

A "galactic year" as defined by astronomers is:

A) the time it takes the Earth to go around the Sun (starting with when it's closest in its orbit to the center of the Galaxy)
B) the time it takes the outermost part of the solar system (the Oort Cloud) to rotate once relative to the Galaxy)
C) the time it took the Milky Way Galaxy to develop spiral arms
D) the time it takes the Sun to revolve once around the center of the Milky Way Galaxy
E) the time it will take the Sun to become a red giant and expand into the Galaxy