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': 'Carrier stage seen in -a)  Poliob)  Cholerac)  Pertusis d) Plague e)  Tetanus \nSelect and explain. \nA. da, B. abc, C. dea, D. ac', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]