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': 'Most immunogenic Typhoid antigen \nSelect and explain. \nA. O antigen, B. H antigen, C. Vi antigen, D. Somatic antigen', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]