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: Social & Preventive Medicine
[{'content': 'Epidemic typhus causes & vector \nSelect and explain. \nA. R. typhi & mite, B. Rickettessia prowazki & louse, C. R. conori & tick, D. R. akari & mite', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]