Why Are the Youngest Galaxies That We See in Distant

Why are the youngest galaxies that we see in distant parts of the universe bluer and brighter than the older galaxies we see closer to us?

A) The red light has been partially absorbed by gas and dust between us and the galaxies.
B) Young galaxies have more dust, and dust scatters blue light better than it scatters red light.
C) The light from the most distant galaxies has been bent by gravitational lenses and focused on Earth.
D) Young galaxies have a burst of star formation that produces many hot, bright, blue stars.