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': 'Trivalent oral polio vaccine contains, type 3 virus: \nSelect and explain. \nA. 300,000 TCID 50, B. 200,000 TCID 50, C. 100,000 TCID 50, D. 400,000 TCID 50', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]