**Core Concept**
Acute post-infective glomerulonephritis (APIN) is a clinical syndrome characterized by the onset of glomerulonephritis following an infection, typically caused by group A beta-hemolytic streptococci. It is a classic example of an immune complex-mediated disease, where the immune system mounts a response against the bacterial antigens, leading to the formation of immune complexes that deposit in the glomeruli.

**Why the Correct Answer is Right**
The correct answer is D. Deposition of IgA. In APIN, the immune complexes that deposit in the glomeruli primarily consist of IgA antibodies. These IgA antibodies are directed against the bacterial antigens, and their deposition in the glomeruli leads to the activation of the complement system, resulting in inflammation and damage to the glomerular capillaries. The deposition of IgA immune complexes is a hallmark of APIN and is responsible for the characteristic histopathological findings in this condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Crescent formation is a feature of rapidly progressive glomerulonephritis (RPGN), which is a different clinical entity characterized by a more severe and rapid progression of renal failure. While crescent formation can occur in APIN, it is not a defining feature of this condition.

**Option B:** Subepithelial deposits are a characteristic feature of membranous nephropathy, a different type of glomerulonephritis that is caused by an autoimmune response against the podocytes. These deposits are not typically seen in APIN.

**Option C:** Granular deposits of IgG can be seen in various types of glomerulonephritis, including IgA nephropathy and lupus nephritis. However, in APIN, the primary immune complex is IgA, and granular deposits of IgG are not a defining feature of this condition.

**Clinical Pearl / High-Yield Fact**
In APIN, the renal biopsy typically shows IgA deposition in the mesangium and along the capillary walls, with a characteristic "starry sky" appearance due to the presence of numerous monocytes and macrophages. This histopathological finding is a key diagnostic clue for APIN.

**✓ Correct Answer: D. Deposition of IgA**