**Core Concept**
Cough is a common adverse effect of angiotensin-converting enzyme (ACE) inhibitors, such as lisinopril, due to their effect on the bronchial epithelium and increased bradykinin levels, which stimulate cough reflexes.

**Why the Correct Answer is Right**
Lisinopril, an ACE inhibitor, blocks the conversion of angiotensin I to angiotensin II and increases bradykinin levels. Bradykinin acts on bradykinin B2 receptors in the airways, leading to increased bronchial sensitivity and a reflex cough. This side effect is particularly common in patients with pre-existing respiratory conditions or those on long-term therapy. The mechanism is well-documented and clinically significant.

**Why Each Wrong Option is Incorrect**
Option B: Propranolol, a non-selective beta-blocker, may reduce bronchial tone but does not cause cough and is not associated with a direct cough mechanism.
Option C: Verapamil, a calcium channel blocker, is used in hypertension and angina and is not linked to cough.
Option D: Sodium nitroprusside, a vasodilator, causes hypotension and can lead to reflex tachycardia or headache, but not cough.

**Clinical Pearl / High-Yield Fact**
ACE inhibitors like lisinopril are the most common cause of cough in patients on antihypertensive therapy. If a patient develops a persistent cough while on an ACE inhibitor, it should be considered a red flag, and the drug may need to be switched to an ARB or alternative therapy.

✓ Correct Answer: A. Lisinopril