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: Medicine
[{'content': 'Which is the usual marker for detection of hepatitis- \nSelect and explain. \nA. HBs Ag, B. HBs Ab, C. HBc Ag, D. HBc Ab', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]