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': 'All of the following are of the size of adult at birth except - \nSelect and explain. \nA. Tympanic membrane, B. Ossicle, C. Cochlea, D. Mastoid process', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]