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': 'Epidemiological marker of Hepatitis – B is \nSelect and explain. \nA. HBs Ag, B. Anti - HBs, C. Anti HBc, D. HBe Ag', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]