**Core Concept**
Pheochromocytoma is a rare, catecholamine-secreting tumor of the adrenal gland, leading to hypertension and other systemic symptoms. The management of pheochromocytoma involves preoperative medical preparation to control blood pressure and prevent hypertensive crises.

**Why the Correct Answer is Right**
The drug of choice in pheochromocytoma is a non-selective alpha and beta blocker, **phenoxybenzamine**, which is a long-acting imidazoline derivative. Phenoxybenzamine blocks alpha receptors, reducing peripheral vascular resistance and preventing hypertensive crises. It also blocks beta receptors, reducing the negative inotropic and chronotropic effects of catecholamines. This allows for more controlled preoperative management and reduces the risk of hypertensive crises during surgery.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **nitroprusside** is a potent vasodilator that may worsen hypotension and is not suitable for preoperative management of pheochromocytoma.
**Option B:** This option is incorrect because **propranolol** is a non-selective beta blocker that does not address the alpha receptor-mediated vasoconstriction in pheochromocytoma.
**Option C:** This option is incorrect because **metoprolol** is a selective beta-1 blocker that may not provide adequate blockade of alpha receptors and may worsen hypertensive crises.

**Clinical Pearl / High-Yield Fact**
The "rule of twos" in pheochromocytoma management states that patients should be started on **two** types of antihypertensive agents: an alpha blocker and a beta blocker, and that **two** liters of fluid should be administered before surgery to prevent hypertensive crises.

**Correct Answer: A. Phenoxybenzamine**