The average lifespan of a red blood cell (RBC) is 120 days. This means that on average, an RBC will live for 120 days before it is destroyed by the body. RBCs are produced in the bone marrow and are responsible for carrying oxygen to the tissues of the body. They are made up of hemoglobin, a protein that contains iron. The iron in hemoglobin binds to oxygen, allowing it to be transported to the tissues. When RBCs reach the end of their lifespan, they are destroyed by the spleen and liver. The iron in the hemoglobin is recycled and used to make new RBCs.
Option A is the correct answer. Option B is incorrect because the average lifespan of an RBC is 120 days, not 99 days. Option C is incorrect because the average lifespan of an RBC is 120 days, not 101 days. Option D is incorrect because the average lifespan of an RBC is 120 days, not 111 days.