The Stellar Components of the Milky Way Galaxy That Act

The stellar components of the Milky Way Galaxy that act as tracers for the mapping of the spiral arm structure in the Galaxy are

A) bright Population I stars and emission nebulae surrounding them.
B) globular clusters.
C) supernova explosions, because they are very luminous and can be seen through considerable dust and gas.
D) old, red giant stars and white dwarfs.