The Emission Lines in Quasar Spectra Were Difficult to Identify

The emission lines in quasar spectra were difficult to identify initially because

A) no one expected violet and ultraviolet spectral lines to be shifted so far toward the red.
B) the observed emission lines were so broad because of internal motions in the quasar that they were difficult to identify.
C) they appeared to be created by elements that did not exist on Earth.
D) they were very faint and could not be measured accurately.