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': 'Eustachian tube opens into middle ear cavity at- \nSelect and explain. \nA. Anterior walls, B. Hypotympanum, C. Superior surface, D. Posterior wall', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The tympanic end of the eustachian tube is bony and is situated in the anterior wall of middle ear. The pharyngeal end of the\xa0tube is slit like and is situated in the lateral wall of the nasopharynx, 1–1.25 cm behind the posterior end of inferior tubinate.Q\n\n\u200bRef. Dhingra 6/e, p 5, 5/e, p 6; Scott Brown 7/e, Vol. III p 3114 Fig. 225.13', 'role': 'assistant'}]