Which Possible Factor MOST Seriously Limits the Accuracy of Spectroscopic

Multiple Choice

Which possible factor MOST seriously limits the accuracy of spectroscopic parallax?

A) Stars of the same spectral luminosity class can have a range of temperatures.
B) It is difficult to accurately measure angular displacement for distant stars.
C) Stars of the same spectral luminosity class can have a range of absolute magnitudes.
D) It is not possible to accurately classify the spectral luminosity of even a nearby star.