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: Pathology
[{'content': 'Normal adult haemoglobin contains \nSelect and explain. \nA. One alpha chain and one beta chain, B. One alpha chains and two beta chains, C. One beta chains and two alpha chains, D. Two alpha chains and two beta chains', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]