**Core Concept**
The question is testing the student's knowledge of the side effects of antihypertensive medications, specifically sedation. Sedation is a common side effect of certain antihypertensive medications due to their central nervous system depressant properties.

**Why the Correct Answer is Right**
Some antihypertensive medications, such as clonidine and reserpine, have sedative properties due to their ability to stimulate alpha-2 adrenergic receptors in the brain, which leads to a decrease in sympathetic outflow and a subsequent decrease in blood pressure. Clonidine, in particular, is known for its sedative effects, which can be beneficial in patients with hypertension and anxiety.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because beta-blockers, such as propranolol, can actually have a stimulating effect on the central nervous system, leading to insomnia and anxiety in some patients.
* **Option B:** This option is incorrect because diuretics, such as hydrochlorothiazide, primarily work by increasing urine production and do not have a significant sedative effect.
* **Option C:** This option is incorrect because ACE inhibitors, such as lisinopril, are often used to treat hypertension and do not have a significant sedative effect.

**Clinical Pearl / High-Yield Fact**
It's worth noting that some antihypertensive medications, such as clonidine, can have a paradoxical effect in patients with certain underlying medical conditions, such as glaucoma or pheochromocytoma. Always consider the patient's medical history and potential interactions when prescribing antihypertensive medications.

**Correct Answer: C. Reserpine.**