I would say that the most probable answer seems to be a), since HDLs scavange LDLs from the bloodstream and artery walls and other deposits, they are in a way, replacing the LDLs, which are higher cholesterol sources.
The answer is A, because HDL stands for high-density lipoproteins. It is sometimes called the "good" cholesterol because it carries cholesterol from other parts of your body back to your liver. Your liver then removes the cholesterol from your body.