Three Different Proteins, A, B, and C, from a Plant

Three different proteins, A, B, and C, from a plant were studied.In each case, a glycine residue was changed to an alanine.Changes in the biological activities of the mutated proteins were then measured, and the results are shown in the table below. Which statement about structure-function relationships in proteins is supported by the data?

A) Each unique amino acid sequence results in a protein with a unique function.
B) A protein's function changes only when changes in primary structure alter its tertiary structure.
C) Substitution of a nonpolar amino acid for another nonpolar amino acid is sufficient to allow a protein to retain its biological activity.
D) Amino acids located at the beginning of a polypeptide chain have less importance in determining biological function than amino acids in the middle or far end of the chain.
E) Every amino acid substitution in a protein's primary structure leads to a change in the protein's function.