**Core Concept:**
The O2 dissociation curve describes the relationship between the partial pressure of oxygen (O2) and the fraction of oxygen molecules bound to hemoglobin (Hb) in the blood. The curve is essential for understanding the affinity of hemoglobin for oxygen and its implications on oxygen transport and binding.

**Why the Correct Answer is Right:**
The correct answer is **C**:

**Clinical Pearl:**
The high affinity of hemoglobin for oxygen at low partial pressures is crucial for maintaining adequate oxygen delivery in the environment of low partial pressures, like high altitude. At high partial pressures, the low affinity of hemoglobin for oxygen prevents oxygen overload and its associated complications.

**Why Each Wrong Option is Incorrect:**
A. This answer is incorrect because it does not address the concept of high affinity at low partial pressures and low affinity at high partial pressures.
B. Although this answer discusses the Hill equation, it does not focus on the right aspect of the curve (affinity changes).
D. This answer emphasizes the Hill equation, but does not emphasize the key aspect of O2 dissociation curve: affinity changes.

**Correct Answer: C. Hemoglobin exhibits high affinity for oxygen at low partial pressures (low oxygen saturation) and low affinity at high partial pressures (high oxygen saturation). This is crucial for maintaining adequate oxygen delivery and preventing complications in different physiological settings.**