Absorption lines in quasars usually have lower redshifts than the quasars themselves do.This suggests that the absorption lines are caused by gas

Question

Quizplus · Accepted Answer

The fact that the absorption lines have lower redshifts than the quasars themselves suggests that the gas causing the absorption is between us and the quasars. This is known as intervening absorption. If the gas causing the absorption were at the same distance as the quasar (option A) it would have the same redshift, and if it were farther away (option C) it would have a higher redshift. Option D is not correct as the absorption lines are not caused by gas within the quasar itself.

Absorption Lines in Quasars Usually Have Lower Redshifts Than the Quasars