**Core Concept**
The body's ability to adapt to high altitude involves complex physiological changes to compensate for lower oxygen levels. This adaptation process is known as acclimatization.

**Why the Correct Answer is Right**
At high altitude, the body increases red blood cell production to carry more oxygen to tissues. This is achieved through the action of erythropoietin (EPO), a hormone produced by the kidneys in response to hypoxia. EPO stimulates the bone marrow to produce more red blood cells, which in turn increases the oxygen-carrying capacity of the blood. This process is a key adaptation mechanism in individuals who have been acclimatized to high altitude for a long time.

**Why Each Wrong Option is Incorrect**
**Option A:** Decreased red blood cell count is incorrect because, in acclimatized individuals, the body increases red blood cell production to adapt to high altitude.
**Option B:** Increased blood pressure is not a direct adaptation to high altitude, although it may be seen in some individuals as a secondary effect.
**Option C:** Decreased oxygen consumption is incorrect because the body's metabolic rate may actually increase in response to high altitude to compensate for lower oxygen levels.

**Clinical Pearl / High-Yield Fact**
Acclimatization to high altitude is a gradual process that can take several weeks to months to complete. It involves not only an increase in red blood cell production but also changes in breathing rate, cardiac output, and other physiological parameters.

**Correct Answer: A. Increased red blood cell count.**