How does the structure of an amino acid enable it to play its most important roles in cells?

A) Because each amino acid contains a variety of functional groups, they can participate in a wide variety of chemical reactions.
B) It can serve a wide variety of functions in a cell, because it contains the atoms most commonly found in organisms C, H, N, and O).
C) The presence of carboxyl and amino groups gives it the ability to form peptide bonds, and its side chain gives it unique chemical properties.
D) Because both carboxyl and amino groups are present, polymerization is exergonic. In addition, the presence of a side chain makes the molecule water soluble.