Each Is True of Proteins,except One

Each is true of proteins,except one.Which is the exception?

A) Proteins are composed of building blocks called amino acids.
B) The classification of the 20 common amino acids is based on the structure of their amino group.
C) The general structure of an amino acid varies considerably.
D) Amino acids polymerize to form long chains called polypeptides.
E) Amino acids contain strong covalent peptide bonds.