**Core Concept**
In patients with hypertension, diabetes, and proteinuria, the primary goal is to control blood pressure while minimizing the risk of kidney damage. The kidneys filter waste and excess fluids from the blood, and diabetes can damage the blood vessels in the kidneys, leading to proteinuria. In this scenario, an ACE inhibitor like Enalapril is often preferred due to its protective effects on the kidneys.

**Why the Correct Answer is Right**
Enalapril, an angiotensin-converting enzyme (ACE) inhibitor, works by blocking the conversion of angiotensin I to angiotensin II, a potent vasoconstrictor. This leads to vasodilation and a decrease in blood pressure. Additionally, ACE inhibitors have been shown to reduce proteinuria by decreasing the pressure within the glomeruli of the kidneys, thereby slowing the progression of kidney disease. Enalapril is particularly beneficial in patients with diabetes and proteinuria due to its renoprotective effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Furosemide is a loop diuretic that increases urine production but does not address the underlying pathophysiology of kidney damage in diabetes. It may even worsen kidney function if not used judiciously.
**Option B:** Methyldopa is an alpha-2 adrenergic agonist that lowers blood pressure by decreasing sympathetic tone. While it can be used in hypertension, it does not have the same renoprotective effects as Enalapril.
**Option D:** Propranolol is a beta-blocker that lowers blood pressure by decreasing heart rate and contractility. However, it does not address the underlying kidney damage caused by diabetes and may even worsen proteinuria in some cases.

**Clinical Pearl / High-Yield Fact**
When managing patients with hypertension, diabetes, and proteinuria, it is essential to choose an antihypertensive agent that has renoprotective effects. ACE inhibitors like Enalapril are a good choice due to their ability to slow the progression of kidney disease.

**✓ Correct Answer: C. Enalapril**