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: Microbiology
[{'content': 'Marker for acute viral hepatitis caused by HBV: \nSelect and explain. \nA. IgM anti-HBc Ag, B. IgG anti-HBc Ag, C. IgM anti-HBs Ag, D. IgG anti-HBs Ag', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. a. IgM anti-HBcAg', 'role': 'assistant'}]