This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'In quaternary structure, subunits are linked by: \nSelect and explain. \nA. Peptide bonds, B. Disulphide bonds, C. Covalent bonds, D. Non-covalent bonds', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The forces that keep the quaternary structure are hydrogen bonds, electrostatic bonds, hydrophobic bonds and van der Waals forces.\nReference: Vasudevan 7th\xa0 ed, pg 38', 'role': 'assistant'}]