**Core Concept**
Non-proliferative Glomerulonephritis (GN) refers to a group of kidney diseases characterized by the absence of significant glomerular cell proliferation, typically involving changes in the glomerular basement membrane, mesangium, or both. These conditions often result from immune complex deposition or other mechanisms that damage the glomerular structure without causing an influx of inflammatory cells.

**Why the Correct Answer is Right**
The correct answer is related to the definition of Non-proliferative GN, which is characterized by the absence of glomerular cell proliferation. **Focal segmental glomerulosclerosis (FSGS)** is a classic example of a non-proliferative GN, where there is sclerosis of the glomeruli without significant cellular proliferation. The pathogenesis of FSGS often involves podocyte injury and subsequent collapse of the glomerular tuft. However, the other options involve conditions with significant glomerular cell proliferation, which are not characteristic of non-proliferative GN.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because **IgA Nephropathy** typically presents with mesangial proliferation, which is a hallmark of proliferative glomerulonephritis.

**Option B:** This option is incorrect because **Membranous Nephropathy** often involves significant mesangial proliferation and is characterized by the deposition of immune complexes on the glomerular basement membrane, leading to a proliferative response.

**Option C:** This option is incorrect because **Rapidly Progressive Glomerulonephritis (RPGN)** is a clinical syndrome characterized by rapid loss of renal function and is typically associated with significant glomerular cell proliferation and crescent formation.

**Clinical Pearl / High-Yield Fact**
The distinction between proliferative and non-proliferative glomerulonephritis is crucial for understanding the pathogenesis and prognosis of these conditions. Non-proliferative GN often has a more indolent course, whereas proliferative GN tends to be more aggressive and requires prompt treatment.

**Correct Answer: D.**