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': 'Which of the following is used as reference protein in nutrition studies? \nSelect and explain. \nA. Egg, B. Fish, C. Milk, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Egg protein is considered the best because of high biological value and easy digestibility. Thus egg is used as reference protein in nutrition studies. Ref: Park 22nd edition, page 564.', 'role': 'assistant'}]