**Core Concept**
The question is testing the concept of drug interactions related to local anesthesia (LA) and their effects on blood pressure. Specifically, it's about a pharmacological agent that can prolong the action of LA in patients with hypertension.

**Why the Correct Answer is Right**
In patients with hypertension, the vasodilatory effect of LA can cause a significant drop in blood pressure. To counteract this effect, a drug that can prolong the action of LA is needed. The correct answer is **Clonidine**, an alpha-2 adrenergic agonist that can be used to prolong the action of LA in hypertensive patients. Clonidine works by stimulating alpha-2 adrenergic receptors in the brain, which leads to a decrease in the sympathetic outflow and a subsequent decrease in heart rate and blood pressure. By prolonging the action of LA, clonidine can help to reduce the risk of hypotension and its associated complications.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the question and is not a commonly used drug to prolong the action of LA.
* **Option B:** This option is incorrect because it is not a drug that is used to prolong the action of LA in hypertensive patients.
* **Option C:** This option is incorrect because it is not a drug that is used to prolong the action of LA in hypertensive patients.

**Clinical Pearl / High-Yield Fact**
Clonidine can be used to prolong the action of LA in hypertensive patients, but it should be used with caution due to its potential to cause sedation and hypotension.

**Correct Answer:** D. Clonidine