Amino acids mainly differ from each other by the difference in their:

Explanation

Option A is correct.Amino acids mainly differ from each other by the difference in their R-group. The R-group is a side chain that is attached to the alpha carbon of an amino acid. The R-group can be any of 20 different functional groups, which is what gives different amino acids their unique properties. The other options are all common to all amino acids:All amino acids have an amino group (-NH2) attached to their alpha carbon. All amino acids have a carboxyl group (-COOH) attached to their alpha carbon. All amino acids have a hydrogen atom attached to their alpha carbon.