Why Do Many H II Regions Glow with a Prominent

Why do many H II regions glow with a prominent red color?

A) Ionized hydrogen, like neutral hydrogen, has the H_α line as one of its electron transitions.
B) Ionized hydrogen does not emit a red line, but it has a yellow line and a magenta line, and the combination of these produces the sensation of red.
C) Ionized hydrogen cannot be detected directly, so CO is used as a tracer, and CO produces a red line.
D) Neutral hydrogen atoms are formed temporarily in the plasma of an H II region, and they emit the red H_α line.