Given reason , at higher altitudes , people suffere from a disease called anoxia. In the disease, they become weak and cannot think clearly.

Explanation

**Step-by-Step Text Solution:**

1. **Understanding Anoxia**: Anoxia is a condition characterized by a deficiency of oxygen in the body. It can lead to symptoms such as weakness and impaired cognitive function.

2. **Effect of Altitude on Oxygen Levels**: At higher altitudes, the atmospheric pressure decreases. This decrease in pressure affects the partial pressure of oxygen in the air. The partial pressure of a gas is the pressure that gas would exert if it occupied the entire volume by itself.

3. **Partial Pressure of Oxygen**: At sea level, the partial pressure of oxygen is higher compared to that at higher altitudes. For example, at sea level, the partial pressure of oxygen is approximately 21% of the atmospheric pressure, which is sufficient for normal physiological functions.

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