People living at sea level have around `5` million RBC per cubic millimetre of their blood whereas those living at an altitude of `5400` metres have around `8` million. This is because at high altitude.

Options

A. people get pollution free air to breth and more oxygen is availabel
B. atmospheric `O_(2)` level is less and hence more rvcs are needed to absorb the required amount of `O_(2)` to sruvivie
C. there is ore uv radiation which enhanes r bc production
D. people eat more nutritive food there fore more rbcs are formed

Answer

B