When the Intensity of the Cosmic Microwave Background Radiation Is

When the intensity of the cosmic microwave background radiation is plotted against wavelength,what is the shape of the resulting curve?

A) emission lines, strongest and most densely concentrated in the microwave region
B) a composite of many overlapping blackbody curves from gas clouds of different temperatures peaking in the microwaves
C) a blackbody curve modified by many deep, overlapping absorption lines and several emission lines
D) an essentially perfect blackbody spectrum peaking in the microwave region