The answer is of course C, but the belief that B has any truth to it is completely mistaken. In one of the best popular astronomy books ever published, THE ALCHEMY OF THE HEAVENS by Ken Croswell, the author while describing the history of discovery of the details of the Milky Way says, "The arms are bright because they contain extremely luminous stars, such as Rigel and Deneb, whereas the regions between the arms are dark because they have no very luminous stars."
Why do most people believe that the spiral arms contain far more stars than other parts of the galactic disk or no stars at all? The stars between arms are almost all dim. The red dwarfs and white dwarfs that are so dim they aren't even visible in other galaxies make up 80% of the galaxy's stars and orange dwarfs, which Crosswell says "Astronomers cannot see them in most other galaxies, either", make up another 15% = 95% of the stars are dim. The massive stars that make the arms so visible don't even live as long as it takes the density wave to move past them. Then it turns out that because of interstellar dust, a stars light is cut in half only 2500 Lyrs from it.
But that alone does not account for the myth. Our society is a Hollywood culture. Whatever's quick, easy and interesting is all you get. No one cares about accuracy and detail. A galaxy looks like bright arms twisted into a spiral with a central bulge - that must be all there is to it. The astronomy documentary shows won't address this kind of thing because there's no percentage in it. No one cares (they think). I am surprised that colleges don't put out a little more effort, though. They didn't when I attended them.
THE ALCHEMY OF THE HEAVENS by Ken Croswell