**Core Concept**
The question is testing the student's knowledge of ammonia metabolism and its handling in the body. Ammonia is a toxic compound that needs to be converted into a non-toxic form for storage and transportation. The correct answer is related to the process by which ammonia is converted into a less toxic form.

**Why the Correct Answer is Right**
The nontoxic form of ammonia is glutamine, which is formed through the action of the enzyme glutamine synthetase. This enzyme catalyzes the reaction of ammonia with glutamate to form glutamine. Glutamine is a major carrier of ammonia in the blood and is also involved in the urea cycle. The conversion of ammonia to glutamine is an important mechanism for reducing the toxicity of ammonia in the body.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the metabolism or handling of ammonia.
* **Option B:** This option is incorrect because it does not accurately describe the nontoxic form of ammonia.
* **Option D:** This option is incorrect because it does not accurately describe the nontoxic form of ammonia.

**Clinical Pearl / High-Yield Fact**
Glutamine is an important molecule in ammonia metabolism, and its levels can be elevated in conditions such as liver disease, where ammonia handling is impaired.

**Correct Answer:** C. Glutamine.