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': 'Which of the following is NOT a content of medial wall of middle ear: \nSelect and explain. \nA. Oval window, B. Round window, C. Processus cochleariformis, D. Aditus ad antrum', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. (d) Aditus ad antrumReft Dhingra's ENT 6th edj 5-6* Aditus ad antrum is located on posterior wall. It is a doorway to antrum of mastoid.* Antrum is largest mastoid air cell.", 'role': 'assistant'}]