Correct Option: B

Red Blood Cells (RBC) take their origin in the bone marrow. The liver also produces RBC, but only during infancy. The average life span of RBC is about 100120 days. The old, worn out and dead RBC are destroyed mainly in an organ called spleen. Hence, bone marrow is commonly called the cradle of RBC' and spleen is commonly called the 'graveyard of RBC'.