People living at sea level have around 5 million RBCs per cubic millimeter of their blood whereas those living at an altitude of 5400 meters have around 8 million. This is because at high altitude:

Explanation

A. People eat more nutritive food, therefore more RBCs are formed:This statement is not accurate. The number of red blood cells (RBCs) is not primarily determined by dietary intake. RBC production is mainly regulated by the body's need for oxygen. While proper nutrition is essential for overall health, it does not directly lead to a significant increase in RBC count. B. People get pollution-free air to breathe and more oxygen is available:This statement is not accurate. While clean air and increased oxygen availability can have health benefits, they do not directly lead to an increase in RBC count. RBC production is primarily regulated by oxygen levels in the body, not external air quality. C. Atmospheric O2 level is less, and hence more RBCs are needed to absorb the required amount of O2 to survive (Correct Option):This statement is accurate. At high altitudes, the atmospheric oxygen level is lower due to reduced air pressure. To meet the body's oxygen requirements, more red blood cells (RBCs) are produced to enhance oxygen-carrying capacity. This adaptation allows individuals to absorb the required amount of oxygen to survive at high altitudes. D. There is more UV radiation which enhances RBC production: This statement is not accurate. While UV radiation can have some effects on the skin and vitamin D production, it does not directly enhance RBC production. RBC production, primarily regulated by the hormone erythropoietin, responds to oxygen levels in the body. Correct Option: C. Atmospheric O2 level is less, and hence more RBCs are needed to absorb the required amount of O2 to survive. Summary: The correct option is C, which accurately describes the adaptation of increased red blood cell (RBC) production at high altitudes. This adaptation is necessary to absorb the required amount of oxygen due to lower atmospheric oxygen levels at high elevations. The other options do not accurately explain the mechanism of RBC count increase at high altitudes.