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
All are of adult size at bih except? 
Select and explain. 
A. Mastoid antrum, B. Ear Ossicles, C. Tyrnpanic cavity, D. Maxillary antrum
D: Maxillary antrum
Answer: D: Maxillary antrum 
Explanation: The tympanic cavity and mastoid antrum , auditory ossicles and structures of the internal ear are all almost fully developed at bih and subsequently alter little.