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 close a oro antral fistula which of the flaps cannot be used \nSelect and explain. \nA. Buccal Flap, B. Palatal Flap, C. Tongue flap, D. Mucus Flap', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]