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': 'Serum marker after Hepatitis B vaccination ? \nSelect and explain. \nA. Anti-HBsAg, B. Anti-HBeAg, C. Anti-HBcAg, D. HBsAg', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Anti-HBsAg", 'role': 'assistant'}]