_____________ Different Genetically-Encoded Amino Acids Are Found in the Proteins

_____________ different genetically-encoded amino acids are found in the proteins of cells; they are distinguished by___________________ .

A) 22; the location of their carboxyl group
B) 20; the location of their amino group
C) 20; the angles between the central carbon and their side chains, or R-groups
D) 22; the composition of their side chains, or R-groups