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': 'Which among the following is the structure of hemoglobin? \nSelect and explain. \nA. Monomer, B. Homodimer, C. Heterodimer, D. Tetramer', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Hemoglobins are tetramers composed of pairs of two different polypeptide subunits.\nRef: Harper’s illustrated biochemistry. 30th edition page no: 54', 'role': 'assistant'}]