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': 'Proteins are linear polymers of amino acids. They\nfold into compact structures. Sometimes, these folded structures associate to form homo-or hetero¬dimers. Which one of the following refers to this associated form? \nSelect and explain. \nA. Denatured state, B. Molecular aggregation, C. Precipitation, D. Quaternary structure', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]