**Core Concept**
Furosemide is a loop diuretic that acts by inhibiting the sodium-potassium-chloride cotransporter (NKCC2) in the ascending limb of the loop of Henle, leading to increased excretion of sodium, chloride, potassium, and water.

**Why the Correct Answer is Right**
Furosemide binds to the NKCC2 cotransporter in the thick ascending limb of the loop of Henle, preventing the reabsorption of sodium, chloride, and potassium ions. This results in an accumulation of these ions in the lumen of the loop of Henle, increasing the osmotic gradient and promoting the excretion of water. The increased delivery of sodium to the distal tubules and collecting ducts also enhances the secretion of potassium ions, leading to hypokalemia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because furosemide does not primarily act on the proximal convoluted tubule (PCT), where glucose, amino acids, and phosphate reabsorption occur.

**Option B:** This option is incorrect because thiazide diuretics, such as hydrochlorothiazide, act by inhibiting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule, not the loop of Henle.

**Option C:** This option is incorrect because the site of action of amiloride is the collecting duct, where it inhibits the epithelial sodium channel (ENaC), leading to increased sodium excretion.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that loop diuretics like furosemide can cause a significant loss of potassium ions, leading to hypokalemia, which can increase the risk of cardiac arrhythmias. Monitor potassium levels closely in patients receiving loop diuretics, especially those with pre-existing renal impairment.

**Correct Answer: C. Thick ascending limb of the loop of Henle.**