Concept:At high altitudes, lower oxygen availability triggers physiological adaptation.
Explanation:At higher altitudes, the air has lower oxygen concentration.
To compensate, the body increases red blood cell production to carry more oxygen.
Therefore, people living at high altitudes often have a higher red blood cell count.
Thus, Reason (R) correctly explains Assertion (A).
Answer:Option A: Both (A) and (R) are true and (R) is the correct explanation of (A).