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': 'A 33-year-old man has never been vaccinated for hepatitis B. Serologic tests reveal negative hepatitis B surface antigen (HBsAg) and positive antibody to surface antigen. Which of the following conditions does this serologic pattern best fit with? \nSelect and explain. \nA. previous hepatitis B infection, B. chronic active hepatitis, C. acute hepatitis B infection, D. poor prognosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The antibody can be demonstrated in 80-90% of patients, usually late in convalescence, and indicates relative or absolute immunity. In contrast, HBsAg occurs very early and disappears in < 6 months. Persistence of HBsAg indicates chronic infection. The pattern in this patient is also seen postvaccination, and perhaps as a consequence of remote infection.', 'role': 'assistant'}]