A Star Cluster at a Great Distance from the Sun

A star cluster at a great distance from the Sun, but inside the Milky Way, appears to be fainter than a similar star cluster at a closer distance. Part of this is the expected result from the inverse square law, but the distant cluster will also appear fainter than expected by distance alone because

A) the photons of light become "tired" and appear less bright as they travel.
B) the cosmological redshift has moved some of the light into the infrared spectral region.
C) star clusters are systematically smaller and hence less bright the farther they are from the galactic center and hence from the Sun.
D) light is scattered and absorbed by interstellar dust and gas between distant clusters and Earth.