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': 'A 24 year-old cook in a hostel mess suffered from enteric fever 2 years back. The chronic carrier state in this patient can be diagnosed by - \nSelect and explain. \nA. Vi agglutination test., B. Blood Culture in Brain Heart infusion broth., C. Widal test, D. All of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Vi agglutinins of titer of > 1:10 is taken significant for diagnosis of Typhoidal carriers', 'role': 'assistant'}]