- Hemoglobin is the protein in red blood cells responsible for transporting oxygen from the lungs to the body's tissues. - Myoglobin (Option B) is also an oxygen binding protein found in muscle tissue, where it stores oxygen for use during muscle activity. - Hemerythrin (Option C) is an oxygen binding protein found in some marine invertebrates but is not present in humans. - Option D ("All of the above") is incorrect because Hemerythrin is not found in the human body. - While both Hemoglobin and Myoglobin bind oxygen in the human body, Hemoglobin is the main protein for systemic oxygen transport via the bloodstream. Given the options, Hemoglobin is the most prominent oxygen binding protein in the body's circulatory system.