**Core Concept**
The question requires the identification of an antihypertensive drug suitable for diabetic patients, considering the potential effects of antihypertensive medications on glucose metabolism and renal function.

**Why the Correct Answer is Right**
The correct answer is **C. Enalapril**. Enalapril is an angiotensin-converting enzyme (ACE) inhibitor, which is often recommended as the first-line antihypertensive agent in diabetic patients. ACE inhibitors work by blocking the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor, thereby reducing blood pressure. Additionally, ACE inhibitors have been shown to have protective effects on the kidneys by reducing proteinuria and slowing the progression of diabetic nephropathy. This is particularly beneficial for diabetic patients, who are at increased risk of developing kidney disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Not specified.
**Option B:** Not specified.
**Option D:** Not specified.

**Clinical Pearl / High-Yield Fact**
ACE inhibitors are preferred in diabetic patients due to their protective effects on the kidneys and their ability to reduce proteinuria, which can slow the progression of diabetic nephropathy.

**Correct Answer:** C. Enalapril.