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': 'Which is most dangerous for transmitting plague- \nSelect and explain. \nA. Blocked flea, B. Partial blocked flea, C. Both, D. Unblocked flea', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]