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 strain which is used for production of BCG vaccine at commercial level is \nSelect and explain. \nA. Danish-1331, B. Tween-80, C. Bacille Calmette Guerin, D. PPD-RT-23', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]