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: ENT
[{'content': 'Which structure prevents spread of infection form middle ear to brain ? \nSelect and explain. \nA. Tegmen tympani, B. Cribriform plate, C. Fundus tympani, D. Petrous apex', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Tegmen tympani Tegmen tympani (forming the roof of middle ear cavity) separates the tympanic cavity from middle cranial fossa.", 'role': 'assistant'}]