Answer: D). An amino acid
Explanation: All Amino acids have a carboxyl group (COOH), an amino acid group (NH2) and a side chain. The side chain is what distinguishes one amino acid from another. Some side chains are polar, hydrophobic, non polar and aromatic in nature. The carboxyl group is what classifies them as acids while the amino group (amine) is what gives them the name "amino".
