**Core Concept**
The question is testing the student's knowledge of amino acid structure, specifically the types of side chains found in amino acids. Amino acids are the building blocks of proteins, and understanding their structure is crucial for understanding protein function and interactions.

**Why the Correct Answer is Right**
The correct answer is a specific type of amino acid that has an iminoside chain, also known as a non-standard amino acid. Iminoside chains are characterized by a nitrogen atom bonded to a carbon atom, which is then bonded to a carbonyl group. This type of side chain is found in a specific amino acid that is not one of the standard 20 amino acids.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not refer to an amino acid with an iminoside chain.
* **Option B:** This option is incorrect because it refers to a standard amino acid, not a non-standard amino acid with an iminoside chain.
* **Option C:** This option is incorrect because it does not match the description of an amino acid with an iminoside chain.

**Clinical Pearl / High-Yield Fact**
The presence of an iminoside chain in an amino acid can have significant implications for protein function and interactions. For example, certain non-standard amino acids can be involved in post-translational modifications that affect protein stability or function.

**Correct Answer: D. Proline**