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 eat more nutritive food, therefore more RBCs are formed
B. people get pollution-free air to breathe and more oxygen is available
C. atmospheric `O_(2)` level is less and hence more `RBCs` are needed to abosorb the required amount of `O_(2)` to survive
D. there is more UV radiation which enhances RBC production.

Answer

C

Explanation

Number of RBCs per cubic millimetre of blood is likely to be higher in people living at high altitudes. This is in response to the air being less dense ahigh altitude and thus more RBCs (and hence more Hb) are needed to absorb the required amount of `O_(2)` from the air having low `PO_(2)`.