Hemoglobin consists of four globular proteins, each formed from a polypeptide chain. Each globular protein contains a nonprotein group with an iron ion. This iron ion binds to an oxygen molecule. Thus, every hemoglobin protein can bind four oxygen molecules. Select the correct statement about oxygen transport below.

A. Myoglobin transports oxygen through the bloodstream to tissue.
B. To carry oxygen, iron must be in its nonheme form.
C. Erythrocytes contain abundant myoglobin for transporting oxygen.
D. Hemoglobin is found in red blood cells, which transport oxygen to tissues