**Core Concept**
The chemical regulation of respiration is primarily controlled by the pH levels in the blood, specifically the concentration of hydrogen ions (H+). This is achieved through the Bohr effect, where an increase in carbon dioxide (CO2) and a decrease in oxygen (O2) levels lead to a decrease in pH, stimulating an increase in ventilation.

**Why the Correct Answer is Right**
The correct answer is related to the regulation of respiration through the chemoreceptors located in the medulla oblongata and the carotid and aortic bodies. These chemoreceptors detect changes in the levels of CO2, O2, and pH in the blood, triggering a response to adjust ventilation accordingly. The Bohr effect, as mentioned earlier, is a key mechanism in this process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the levels of carbon dioxide (CO2) do indeed affect the chemical regulation of respiration, as explained by the Bohr effect.

**Option B:** This option is incorrect as the levels of oxygen (O2) also play a crucial role in regulating respiration, particularly in the peripheral chemoreceptors.

**Option D:** This option is incorrect as the levels of hydrogen ions (H+) are directly related to the pH levels in the blood, which in turn affect the chemical regulation of respiration.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the Bohr effect is a critical mechanism in the regulation of respiration, and an understanding of this concept is vital for managing patients with respiratory or cardiac conditions.

**Correct Answer: None**