**Core Concept**
In the context of preeclampsia, a hypertensive emergency refers to a severe increase in blood pressure that poses an immediate threat to the mother or fetus. The management of hypertensive emergencies in preeclampsia involves the use of antihypertensive medications to rapidly lower blood pressure and prevent complications.

**Why the Correct Answer is Right**
The goal of antihypertensive therapy in preeclampsia is to lower blood pressure while maintaining uteroplacental perfusion. Nitroprusside, **Option B** (sodium nitroprusside), is a potent vasodilator that can rapidly lower blood pressure. It acts by releasing nitric oxide, which relaxes vascular smooth muscle and reduces blood pressure. Captopril, **Option C** (angiotensin-converting enzyme inhibitor), is also used to manage hypertension in preeclampsia. It blocks the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, thereby reducing blood pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** Labetalol is not typically used in hypertensive emergencies in preeclampsia due to its slower onset of action and potential for reflex tachycardia.
* **Option D:** Hydralazine is commonly used to manage hypertensive emergencies in preeclampsia, but it is not the only option listed.

**Clinical Pearl / High-Yield Fact**
In the management of hypertensive emergencies in preeclampsia, it's essential to remember that the goal is to rapidly lower blood pressure while maintaining uteroplacental perfusion. The choice of antihypertensive agent should be guided by the severity of hypertension and the presence of any co-existing medical conditions.

**Correct Answer: A. Labetalol**