The correct answer is their blood lacks A or B antibodies.
People with type AB blood have A and B antigenes on the surface of red blood cells (RBCs). Antigen AB has no antibodies, thus, transfusion can be considered safe ( the serum of the recipient does not contain antibodies for the blood cell antigens of the donor).
Answer:
The alveolar walls and capillary walls share a membrane. That's how close they're getting. This allows oxygen and carbon dioxide to readily pass from the respiratory system to the circulation. Oxygen molecules bind to red blood cells as they return to the heart.