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 the spread of infection from the middle ear to the brain \nSelect and explain. \nA. Tegmen tympani, B. Cribriform plate, C. Fundus tympani, D. Petrous apex', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Tegmen tympani forms the roof of the middle ear and it also extends posteriorly to form a roof of aditus and antrum.', 'role': 'assistant'}]