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
All of the following are of the size of adult at birth except - 
Select and explain. 
A. Tympanic membrane, B. Ossicle, C. Cochlea, D. Mastoid process
D: Mastoid process
Answer: D: Mastoid process 
Explanation: None