The correct answer for this question is option 2, the spleen. The spleen is known as the graveyard of red blood cells (RBCs). This is because the spleen plays a crucial role in removing old or damaged RBCs from circulation. It filters the blood and identifies and breaks down these aging or defective RBCs. The spleen contains specialized cells called macrophages, which engulf and digest the damaged RBCs. These macrophages also recycle the iron and other components of the breakdown products, returning them to the body for reuse. This process helps to maintain a healthy population of functional RBCs in the bloodstream. The liver (option 1), brain (option 3), and heart (option 4) do not perform the same function as the spleen in eliminating old RBCs.