**Core Concept**
Post streptococcal glomerulonephritis (PSGN) is an immune complex-mediated glomerulonephritis that occurs following a streptococcal infection. It is characterized by the deposition of immune complexes in the glomeruli, leading to an inflammatory response and damage to the glomerular capillaries.

**Why the Correct Answer is Right**
The probable diagnosis is PSGN due to the presence of subepithelial humps and the characteristic "starry sky" appearance on histopathology. This is caused by the deposition of immune complexes, which trigger an inflammatory response and lead to the proliferation of mesangial cells and the formation of subepithelial humps. The "starry sky" appearance is due to the presence of scattered, activated macrophages that have ingested the immune complexes.

**Why Each Wrong Option is Incorrect**
**Option A:** Membranoproliferative GN is characterized by the thickening of the glomerular basement membrane and the proliferation of mesangial cells, but it does not typically present with subepithelial humps or a "starry sky" appearance.

**Option B:** Rapidly proliferative GN is characterized by the rapid onset of glomerulonephritis, often with severe oliguria and hematuria, but it does not typically present with subepithelial humps or a "starry sky" appearance.

**Option D:** Diabetic nephropathy is characterized by the thickening of the glomerular basement membrane and the accumulation of extracellular matrix, but it does not typically present with subepithelial humps or a "starry sky" appearance.

**Clinical Pearl / High-Yield Fact**
PSGN is often preceded by a streptococcal infection, such as strep throat or skin infection, and may present with hematuria, proteinuria, and hypertension.

**✓ Correct Answer:** C. Post streptococcal glomerulonephritis