This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Medicine
[{'content': 'Marker for active HBV ? \nSelect and explain. \nA. HBsAg, B. HBcAg, C. JgM anti HBSAg, D. IgG anti HBSAg', 'role': 'user'}, {'content': 'Answer: A \nExplanation: <P>Davidson&;s principles and practice of medicine 22nd edition. *HBs Ag is an indicator of active infection and a negative test for HBs Ag makes HBV infection very unlikely.HBcAg is not found in blood but antibody to it appeared in the blood.</p>', 'role': 'assistant'}]