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': 'No chemoprophylaxis for - a)  Typhoidb)  Chicken poxc)  Influenzad)  Cholera \nSelect and explain. \nA. b, B. ab, C. ab, D. bd', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]