How Does the Interstellar Medium Obscure Our View of Most

How does the interstellar medium obscure our view of most of the galaxy?

A) Molecules in the interstellar medium absorb all wavelengths of light.
B) Hydrogen gas produces so much visible light that the interstellar medium is opaque, blocking our view of anything beyond it.
C) The small mixture of dust grains in the interstellar medium absorbs visible light.
D) Dust reflects most light from distant regions of the galaxy back towards the source.
E) all of the above