This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ear, Subject name: ENT
[{'content': 'Operation of choice for coalescent mastoiditis is: \nSelect and explain. \nA. Cortical mastoidectomy, B. Modified radical mastoidectomy, C. Radical mastoidectomy, D. Fenestration operation', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Coalescent mastoiditis is treated by cortical mastoidectomy, also known as Schwartz operation. In this operation all mastoid air cells are exenterated leaving posterior canal wall intact.', 'role': 'assistant'}]