Answer :
Answer: Option D.
Explanation:
Protein are large biomolecules which contains one or more long chains of amino acid residues and plays important functions in living organism.
Proteins consist of one or more than one polypeptide chains.
If proteins consist of only one polypeptide chain they form primary structure, secondary, and tertiary structures while if a protein consist of more than one polypeptide chain it forms Quaternary structure.
Proteins with multiple polypeptide chains called subunits and these subunits attach together to give Quaternary structure. Multiple polypeptides chains are arranged in folded protein subunits and allows formation of simple dimers and large complexes with different numbers of subunits. Examples of Quaternary structure d proteins are DNA polymerase, hemoglobin, and ion channels.
Hence, the correct option is D.