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