At high altitudes, the oxygen content of the air can be only a third of the amount at sea level. As a person makes a gradual climb up a mountain, the body slowly adapts to the high altitude. What is increased during this time of adjustment?
- Athe concentration of haemoglobin in the red blood cells
- Bthe oxygen-carrying capacity of the haemoglobin
- Cthe number of red blood cells per $\text{mm}^3$ of blood
- Dthe rate at which haemoglobin releases oxygen into the tissues