It has been found that people living in at higher altitudes have many more red blood corpuscles in their blood than people living in plains. Which one of the following best accounts for their phenomenon ? 

A) The cold climate stimulates the production of red blood corpuscles to keep the body warm. 

B) People of high mountains breathe more quickly. 

C) The low air pressure requires more red blood corpuscles to supply the body cells with oxygen. 

D) The low air pressure in high mountains speeds up the blood circulation so that more red blood corpuscles are needed.