**Core Concept**
The question is based on the relationship between partial pressure of oxygen (PO2) and hemoglobin (Hb) saturation. This relationship is crucial in understanding oxygen transport in the blood. The **oxygen-hemoglobin dissociation curve** is a graphical representation of this relationship.

**Why the Correct Answer is Right**
A PO2 of over 8kPa corresponds to a point on the oxygen-hemoglobin dissociation curve where hemoglobin is nearly fully saturated with oxygen. At this partial pressure, the **hemoglobin** molecules are mostly bound to oxygen, indicating a high **oxygen saturation**. This is because the curve reaches a plateau at high PO2 values, where increasing PO2 does not significantly increase Hb saturation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option would be incorrect because a PO2 of over 8kPa does not correspond to the beginning of the curve where saturation starts to increase.
**Option B:** This option is also incorrect as it does not accurately describe the relationship between PO2 and Hb saturation at this level.
**Option C:** Similarly, this option does not correctly represent the point on the curve where PO2 is over 8kPa.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the oxygen-hemoglobin dissociation curve is **S-shaped**, with the steep part of the curve occurring at lower PO2 levels, indicating the range where small changes in PO2 significantly affect Hb saturation.

**Correct Answer:** D. nearly 100%