**Core Concept**
Bilaterally enlarged kidneys can result from various conditions that lead to an increase in renal size, often due to an accumulation of fluid, fibrosis, or cellular proliferation. This can be caused by systemic diseases, metabolic disorders, or as a consequence of renal injury.

**Why the Correct Answer is Right**
The correct answer is a condition characterized by the deposition of abnormal proteins in the kidneys, leading to their enlargement. This condition is associated with the accumulation of amyloid fibrils in the renal interstitium, which disrupts the normal architecture of the kidneys and impairs their function. The amyloid deposits can be seen on renal biopsy and are often accompanied by proteinuria and progressive renal failure.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a condition that typically presents with unilaterally enlarged kidneys, often due to obstruction of the urinary tract. While it can lead to renal enlargement, it is not associated with bilateral kidney enlargement.

**Option B:** This option is incorrect because it is a condition that typically presents with normal-sized kidneys, often due to the destruction of renal tissue. While it can lead to renal failure, it is not associated with bilateral kidney enlargement.

**Option C:** This option is incorrect because it is a condition that typically presents with normal-sized kidneys, often due to an autoimmune response against the kidneys. While it can lead to renal failure, it is not associated with bilateral kidney enlargement.

**Clinical Pearl / High-Yield Fact**
A key feature of conditions that lead to bilaterally enlarged kidneys is the presence of systemic symptoms, such as weight loss, fatigue, and proteinuria. A high index of suspicion is necessary to diagnose these conditions, and renal biopsy may be required to confirm the diagnosis.

**Correct Answer: C. Amyloidosis.**