Which one of the following human organs is often called the "graveyard" of RBCs?

Old red blood cells are recycled in the spleen, so it is called "graveyard of RBC". The RBCs are mechanically filtered in the red pulp portion of the spleen and after the filtration, the old RBCs are recycled. The spleen plays important roles in regard to red blood cells (also referred to as erythrocytes) and the immune system. It removes old red blood cells and holds a reserve of blood, which can be valuable in case of hemorrhagic shock, and also recycles iron. So, the correct answer is option B.