## **Core Concept**
The question pertains to the likely renal pathology following an episode of **Upper Respiratory Infection (URI)**, presenting with **gross hematuria**. This scenario suggests a condition that correlates with or is precipitated by infections, leading to renal involvement.

## **Why the Correct Answer is Right**
The correct answer, **C. Post-streptococcal glomerulonephritis (PSGN)**, is right because PSGN is a well-known complication that can occur after an upper respiratory tract infection (or skin infection) caused by certain strains of streptococci. This condition is characterized by the deposition of immune complexes in the glomeruli, leading to inflammation and damage, which manifests clinically as hematuria, proteinuria, and sometimes renal failure. The timing of 3 days after the URI is consistent with the typical latency period for PSGN to develop.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, incorrect options might include conditions not directly related to post-infectious glomerulonephritis or not commonly associated with URI and hematuria.
- **Option B:** Similarly, without the specific content of Option B, we can infer that any condition not directly linked to the immune complex deposition following an infection or not commonly presenting with hematuria post-URI would be incorrect.
- **Option D:** This would be incorrect if it represents a condition not associated with the clinical presentation of hematuria following an URI, such as a simple urinary tract infection or a condition not typically linked to immune complex deposition.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Post-streptococcal glomerulonephritis (PSGN)** typically presents with **hematuria**, **proteinuria**, and sometimes **hypertension** following an **upper respiratory or skin infection**. The classic triad of PSGN includes hematuria, proteinuria, and azotemia. PSGN usually has a good prognosis, especially in children, but can have a more severe course in adults.

## **Correct Answer:** C. Post-streptococcal glomerulonephritis.