This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Secondary, Tertiary and Quaternary Structure of Proteins, Subject name: Biochemistry
Quaternary structure of protein is: 
Select and explain. 
A. The arrangement sequence of amino acids in the polypeptide chain, B. Inter relation between amino acids in a single polypeptide chain, C. Inter relation of amino acid in 2 polypeptide chains, D. The inter relation and arrangement of polypeptides in a protein with more than 2 polypeptides chains
D: The inter relation and arrangement of polypeptides in a protein with more than 2 polypeptides chains
Answer: D: The inter relation and arrangement of polypeptides in a protein with more than 2 polypeptides chains 
Explanation: Ans. D. The inter relation and arrangement of a polypeptides in the protein with more than 2 polypeptides chains)a. Protein that contain two or more polypeptide chains associated by non-covalent forces are said tob. exhibit quaternary structure.c. The arrangement sequence of amino-acids in the polypeptide chain -- is primary structure of protein.d. Inter relation of amino-acids in polypeptide chain is -- secondary structure.