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': 'Length of external auditory canal is ______________ \nSelect and explain. \nA. 12 mm, B. 24 mm, C. 36 mm, D. 48 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. 24 mm In adults the external acoustic meatus measures about 24 mm from the introitus to the tympanic membrane, which is its medial limit.', 'role': 'assistant'}]