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': 'Prophylaxis for health personnel working in a plague ward is -a) Vaccineb) Tetracycline throughout the dutyc) A cource of tetracyclined) Vaccine and Erythromycine) Observation \nSelect and explain. \nA. ac, B. a, C. ab, D. bc', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]