The Rings of Material Surrounding the SN 1987A Remnant Glow $\alpha$

The rings of material surrounding the SN 1987A remnant glow. In what region of the spectrum do they emit most of their radiation?

A) The rings are mostly hydrogen shed from the star's envelope, so the H _$\alpha$ line might be expected to be prominent in the resulting spectrum.
B) The rings glow because of natural radioactivity, which emits mostly gamma radiation.
C) The heavy elements created in the supernova have complex atomic structures that emit a continuous spectrum.
D) Only the longest radio waves can penetrate the dust clouds surrounding the supernova remnant.