**Core Concept**
Furosemide is a loop diuretic that acts on the ascending limb of the loop of Henle in the kidneys to increase urine production. It is primarily used to treat edema associated with congestive heart failure, liver disease, and nephrotic syndrome.

**Why the Correct Answer is Right**
Furosemide is a potent loop diuretic that is often used in the management of acute pulmonary edema due to its rapid onset of action and ability to produce a significant diuretic effect. The drug works by inhibiting the sodium-potassium-chloride cotransporter (NKCC2) in the thick ascending limb of the loop of Henle, leading to a decrease in sodium and chloride reabsorption and an increase in urine production. This mechanism is particularly effective in reducing pulmonary congestion and improving respiratory function in patients with acute pulmonary edema.

**Why Each Wrong Option is Incorrect**
**Option B:** Furosemide acts on the ascending limb of the loop of Henle, not the proximal convoluted tubule (PCT). The PCT is the site of action for other diuretics such as acetazolamide and certain aminoglycosides.
**Option C:** Furosemide is a potent loop diuretic that produces a significant diuretic effect, rather than mild diuresis. It is often used in the management of severe edema and fluid overload.
**Option D:** Furosemide can be administered by both oral and parenteral routes, although the parenteral route is often used in acute settings such as acute pulmonary edema.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that furosemide can cause significant electrolyte imbalances, particularly hypokalemia and hypomagnesemia, due to its effects on potassium and magnesium reabsorption in the kidneys.

**✓ Correct Answer: A. Acute pulmonary edema is an indication**