**Core Concept**
The question is testing the student's knowledge of urea synthesis in the body, specifically the location and mechanism of urea formation. Urea is a waste product formed from the breakdown of amino acids, and its synthesis is a crucial aspect of nitrogen metabolism.

**Why the Correct Answer is Right**
Urea is primarily formed in the liver through the urea cycle, also known as the ornithine cycle. This process involves a series of enzyme-catalyzed reactions that convert ammonia (NH3) into urea, which is then excreted by the kidneys. The key enzymes involved in this process include carbamoyl phosphate synthetase I (CPS I), ornithine transcarbamylase (OTC), and argininosuccinate synthetase (ASS).

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to urea formation.
* **Option B:** This option is incorrect because urea is not formed in the kidneys, but rather in the liver and then excreted by the kidneys.
* **Option C:** This option is incorrect because while the liver is the primary site of urea formation, the kidneys are not directly involved in this process.

**Clinical Pearl / High-Yield Fact**
The urea cycle is a critical process in maintaining nitrogen balance and preventing ammonia toxicity. A deficiency in any of the enzymes involved in the urea cycle can lead to hyperammonemia and neurological symptoms.

**Correct Answer:** C. Liver.