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': "Agglutination with 'O' antigen of S. typhi is inhibited by - \nSelect and explain. \nA. Vi antigen, B. Pili antigen, C. Flagellar antigen, D. All of the above", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]