How does hemoglobin's oxygen binding curve change with varying partial pressures of oxygen, and what are the physiological implications?

• A. Hemoglobin's affinity decreases with higher partial pressures, reducing oxygen delivery to tissues.
• B. Hemoglobin's affinity decreases with lower partial pressures, enhancing oxygen delivery to tissues.
• C. Hemoglobin's affinity remains constant regardless of partial pressure changes.
• D. Hemoglobin's affinity increases with higher partial pressures, enhancing oxygen delivery to tissues.