**Core Concept**
Reflux nephropathy is a condition characterized by chronic kidney damage due to recurrent episodes of vesicoureteral reflux, leading to scarring and impaired renal function. In some cases, this scarring can lead to significant proteinuria, often in the nephrotic range.

**Why the Correct Answer is Right**
The correct answer is associated with a condition where the scarring from reflux nephropathy leads to the obstruction of the urinary tract, causing a backup of urine into the kidneys and further exacerbating the proteinuria. This is often seen in patients with posterior urethral valves, a congenital anomaly that causes obstruction of the urethra. The obstruction leads to increased pressure in the urinary tract, causing the scarring and proteinuria associated with reflux nephropathy.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because while reflux nephropathy can cause significant proteinuria, it is not typically associated with the nephrotic range. The nephrotic range is usually seen in conditions such as minimal change disease or focal segmental glomerulosclerosis.

**Option B:** This is incorrect because while IgA nephropathy can cause significant proteinuria, it is not typically associated with reflux nephropathy or the nephrotic range.

**Option C:** This is incorrect because while membranous nephropathy can cause significant proteinuria, it is not typically associated with reflux nephropathy or the nephrotic range.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that proteinuria in the nephrotic range can be seen in a variety of conditions, including reflux nephropathy, and it is essential to consider the patient's history and clinical presentation when making a diagnosis.

**Correct Answer: C. Posterior urethral valves.**