**Core Concept**
Normal resting ventilation is primarily regulated by the respiratory centers in the brainstem, which respond to various stimuli to maintain an optimal balance between oxygenation and carbon dioxide elimination. The main stimuli for normal resting ventilation include chemical and mechanical factors that influence the respiratory drive.

**Why the Correct Answer is Right**
J receptors, also known as juxtacapillary receptors, are located in the pulmonary capillary bed and are activated by high levels of pulmonary interstitial fluid, hypoxia, and inflammation. They play a crucial role in mediating the ventilatory response to pulmonary edema and other conditions that increase pulmonary capillary pressure. However, they are not involved in the regulation of normal resting ventilation.

**Why Each Wrong Option is Incorrect**
**Option A:** Stretch receptors are mechanoreceptors located in the bronchi and bronchioles that are activated by lung inflation and play a crucial role in regulating the rate and depth of breathing during normal resting ventilation.
**Option C:** PO2 (partial pressure of oxygen) is a key stimulus for ventilation, and hypoxemia (low PO2) can stimulate the respiratory centers to increase ventilation.
**Option D:** PCO2 (partial pressure of carbon dioxide) is another crucial stimulus for ventilation, and hypercapnia (elevated PCO2) can stimulate the respiratory centers to increase ventilation.

**Clinical Pearl / High-Yield Fact**
The Hering-Breuer inflation reflex, mediated by stretch receptors in the lungs, helps to prevent overinflation of the lungs by inhibiting inspiration when the lungs are fully inflated.

**✓ Correct Answer: B. J receptors**