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: Surgery
[{'content': 'During extraction of the upper first molar, the mesio buccal root is missing and is suspected to have been pushed into the maxillary sinus.\nTo classify a chronic oral antral communication what time duration is acceptable? \nSelect and explain. \nA. 7 days, B. 14 days, C. 21 days, D. 28 days', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]