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: Anatomy
[{'content': 'Which of the following attains adult size before birth - \nSelect and explain. \nA. Ear ossicles, B. Maxilla, C. Mastoid, D. Parietal bone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]