The correct option is A have more RBCs and their haemoglobulin has a lower binding affinity to oxygen
Tourists visiting high altitude areas such as Rohtang Pass, experiences altitude sickness. Symptoms are nausea, fatigue and high palpitations. This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen. But, gradually we get acclimatized and stop experiencing altitude sickness. The body compensates low oxygen availability by increasing red blood cells production, decreasing the binding affinity of haemoglobin and by increasing breathing rate.