**Core Concept**
The question is testing the student's knowledge of the chemical properties of amino acids, specifically their side chains. In physiological conditions, amino acids can have different charges due to ionization of their side chains. The question is asking the student to identify amino acids with negatively charged side chains.

**Why the Correct Answer is Right**
Amino acids with negatively charged side chains are those that contain carboxyl (-COO-) or sulfonate (-SO3-) groups. These groups can accept protons (H+ ions) in physiological conditions, resulting in a net negative charge. The correct answer is likely an amino acid with a carboxyl group in its side chain, such as aspartic acid or glutamic acid.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely a neutral amino acid, such as alanine, which does not have a negatively charged side chain.
**Option B:** This option is likely a positively charged amino acid, such as arginine, which has a guanidinium group in its side chain.
**Option C:** This option is likely a non-polar amino acid, such as valine, which does not have a negatively charged side chain.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the charge on an amino acid's side chain can affect its interactions with other molecules, including enzymes and receptors. Understanding the chemical properties of amino acids is crucial for understanding various biological processes, including protein structure and function.

**Correct Answer:** C. Glutamic acid.