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 the external auditory canal is \nSelect and explain. \nA. 20 mm, B. 22 mm, C. 24 mm, D. 15 mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: EXTERNAL AUDITORY CANAL\n\nIt starts at the external auditory meatus and ends at the tympanic membrane, where a bony structure (bony outer attic wall at tympanic membrane, where ECA ends) projects, called scutum.\nIt is almost S-shaped curved canal of about 24 mm length.\nIt has - outer cartilaginous part (2/3rd) and - inner bony part (l/3rd).\nIt is directed upwards, backward and medially in the outer part and downwards, forwards and medially in the inner part.\nThe periosteum is very firmly adherent in EAC and hence even a minor infection like a furuncle is extremely painful.', 'role': 'assistant'}]