People living at sea level have around 5 million RBC per cu.mm of their blood where as those living at an altitude of 5400 metres have around 8 million. This is because at high altitude

Options

A. People eat more nutritive food, therefore more RBC are formed
B. People get pollution free air to breathe and more oxygen is available
C. Atmospheric `O_2` level is less and more RBC are needed to absorb the required amount of `O_2` to survive
D. There is more UV radiation which enhances RBCs production

Answer

C