**Core Concept**
Hypertensive crisis is a severe elevation in blood pressure that requires immediate management to prevent target organ damage. The primary goal is to rapidly lower blood pressure to a safe level while minimizing the risk of adverse effects.

**Why the Correct Answer is Right**
In managing hypertensive crisis, several agents are used based on their mechanism of action and onset of effect. **Nitroprusside**, a potent vasodilator, is often used due to its rapid onset of action, allowing for quick titration to achieve the desired blood pressure. **Labetalol**, a mixed alpha/beta-blocker, is another option as it can be administered intravenously and has a rapid onset of action. **Nicardipine**, a calcium channel blocker, is also used for its rapid onset of action and ability to be titrated to achieve the desired blood pressure reduction. **Enalapril**, an ACE inhibitor, is typically used orally for the management of hypertension but is not typically used in hypertensive crisis due to its slower onset of action.

**Why Each Wrong Option is Incorrect**
**Option A:** Nitroprusside is not the correct answer as it is indeed used in hypertensive crisis. **Option B:** Labetalol is also used in hypertensive crisis, making it an incorrect choice. **Option C:** Nicardipine is another correct option, used in hypertensive crisis. **Option D:** Enalapril, however, is not typically used in hypertensive crisis due to its slower onset of action.

**Clinical Pearl / High-Yield Fact**
In managing hypertensive crisis, it is essential to rapidly lower blood pressure while minimizing the risk of adverse effects. The choice of agent depends on the severity of the crisis, the presence of specific comorbidities, and the patient's overall clinical status.

**Correct Answer:** D. Enalapril.