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': 'Endemic Typhus is caused by: \nSelect and explain. \nA. R. Prowazaki, B. R. Typhi, C. R. Ricketssiae, D. R. Akari', 'role': 'user'}, {'content': 'Answer: B \nExplanation: R. Typhi', 'role': 'assistant'}]