**Core Concept**
The combination of diuretics with ACE inhibitors in patients with hypertension or heart failure requires careful selection to avoid adverse effects, such as hypotension and electrolyte imbalances. The renin-angiotensin-aldosterone system (RAAS) is inhibited by ACE inhibitors, which can lead to increased potassium levels. To counteract this effect, a potassium-wasting diuretic is often used.

**Why the Correct Answer is Right**
Hydrochlorothiazide (HCTZ) is a thiazide diuretic that acts by inhibiting sodium and chloride reabsorption in the distal convoluted tubule, leading to increased potassium excretion. This makes it an ideal combination with ACE inhibitors, which can cause hyperkalemia due to reduced aldosterone levels. By using a potassium-wasting diuretic like HCTZ, the risk of hyperkalemia is mitigated. Additionally, thiazide diuretics like HCTZ also have a mild vasodilatory effect, which can complement the vasodilatory action of ACE inhibitors.

**Why Each Wrong Option is Incorrect**
**Option A:** Spironolactone is a potassium-sparing diuretic that acts as an aldosterone antagonist. Combining it with ACE inhibitors would increase the risk of hyperkalemia, making it an inappropriate choice.
**Option B:** Eplerenone is another potassium-sparing diuretic similar to spironolactone. It would also increase the risk of hyperkalemia when combined with ACE inhibitors, making it an incorrect choice.
**Option D:** Amiloride is a potassium-sparing diuretic that acts by inhibiting the sodium-potassium pump in the collecting duct. Like spironolactone and eplerenone, it would increase the risk of hyperkalemia when combined with ACE inhibitors, making it an incorrect choice.

**Clinical Pearl / High-Yield Fact**
When combining diuretics with ACE inhibitors, always choose a potassium-wasting diuretic to avoid hyperkalemia. Thiazide diuretics like hydrochlorothiazide are ideal for this purpose.

**✓ Correct Answer: C. Hydrochlorothiazide**