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
Length of external auditory canal is: 
Select and explain. 
A. 12 mm, B. 24 mm, C. 36 mm, D. 48 mm
B: 24 mm
Answer: B: 24 mm 
Explanation: 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.