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: Social & Preventive Medicine
[{'content': "The reference protein is \nSelect and explain. \nA. Cow's milk, B. Hen's Egg, C. Meat, D. Fish", 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]