During exercise, skeletal muscle tissues experience a decrease in local partial pressure of oxygen. According to the oxygen dissociation curve, why does hemoglobin release oxygen more readily under these conditions?

Reduced oxygen binding to one heme group lowers hemoglobin affinity and promotes additional oxygen release

Lower oxygen levels cause hemoglobin to gain extra oxygen-binding sites

Oxygen release occurs only after all four oxygen molecules detach simultaneously

Hemoglobin affinity for oxygen increases as tissue oxygen levels decrease