When Making a Spectrum of a Distant Galaxy, It Is

When making a spectrum of a distant galaxy, it is usual practice to allow light from a laboratory sample of some element, say neon, to fall upon the spectrum as well. Why is this done?

A) The known positions of the neon spectrum lines allow the spectrum to be calibrated so that the wavelengths of the lines from the galaxy can be determined.
B) The emission lines from the laboratory neon will fill in the absorption lines from neon in our atmosphere, thus getting rid of these lines so that they are not confused with lines from the galaxy.
C) The laboratory neon lines show the maximum velocity position of neon. These laboratory neon lines can then be compared with neon lines from the galaxy spectrum so the Doppler shift based on neon can be calculated.
D) The procedure is just a test to assure that the system is working properly without distortion before the galaxy spectrum is analyzed.