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 is a live vaccine: \nSelect and explain. \nA. BCG, B. Salk, C. DPT, D. Tetanus toxoid', 'role': 'user'}, {'content': 'Answer: A \nExplanation: BCG', 'role': 'assistant'}]