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': 'The characteristics of polio vaccine are all except- \nSelect and explain. \nA. Maintenance of cold chain, B. 100 % immunisation, C. Killed vaccine is effective in India, D. 5 doses of OPV given', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]