Answer is: D. more than ten amino acids joined by peptide bonds.
Polypeptide is a long and unbranched peptide chain with more than ten amino acids.
Proteins consist of one or more polypeptides arranged in a biologically functional way.
Peptide bond is a covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another along a peptide or protein chain.
