What Effect Do Even Thin Clouds of Dust Have on Light

What effect do even thin clouds of dust have on light passing through them?

A) The light that passes though them is blue shifted due to the cloud's approach.
B) It dims the light of all more distant stars.
C) Even a little can completely block all light, such as the Horsehead Nebula.
D) Its motion causes the light of stars beyond to twinkle.
E) Its motion causes all light to be redshifted as it passes through these clouds.