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: External auditory canal of an adult is 24 mm in length. Outer one-third (8 mm) is cailaginous and inner two thirds (16 mm) are bony. Cailaginous pa contains hair preventing proper visualization of drum.', 'role': 'assistant'}]