**Core Concept**
The bronchial arteries are a pair of arteries that arise from the aorta and supply oxygenated blood to the airways, including the bronchi, bronchioles, and associated connective tissue. They are part of the pulmonary circulation and are responsible for supplying the bronchial tree with blood.

**Why the Correct Answer is Right**
The alveolar sacs, which are the final structures in the respiratory pathway where gas exchange occurs, receive their blood supply from the pulmonary arteries, not the bronchial arteries. The pulmonary arteries branch off from the pulmonary trunk and distribute oxygenated blood from the lungs to the alveoli. In contrast, the bronchial arteries supply the airway walls, including the bronchi and bronchioles, as well as the surrounding connective tissue. This distinction is critical in understanding the anatomy of the respiratory system.

**Why Each Wrong Option is Incorrect**
**Option A:** The bronchial arteries do supply the bronchi, which are the larger airways that branch off from the trachea. They provide oxygenated blood to the mucosal lining and associated connective tissue.
**Option B:** Bronchioles, which are smaller airways that branch off from the bronchi, also receive their blood supply from the bronchial arteries. This includes the muscular and glandular components of the bronchioles.
**Option C:** The alveolar ducts, which lead to the alveoli, receive their blood supply from the bronchial arteries, which then branch off to the pulmonary arteries. This is because the bronchial arteries are responsible for supplying the airway walls, including the alveolar ducts.

**Clinical Pearl / High-Yield Fact**
In the context of respiratory medicine, it's essential to remember that the bronchial arteries are responsible for supplying the airway walls, including the bronchi and bronchioles, whereas the pulmonary arteries supply the alveoli and associated connective tissue. This distinction is critical in understanding the pathophysiology of various respiratory conditions.

**✓ Correct Answer: D. Alveolar sac. The alveolar sacs are the final structures in the respiratory pathway where gas exchange occurs, and they receive their blood supply from the pulmonary arteries, not the bronchial arteries.**