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
First sinus developed: 
Select and explain. 
A. Maxillary sinus, B. Frontal sinus, C. Sphenoidal sinus, D. Ethmoidal sinus
A: Maxillary sinus
Answer: A: Maxillary sinus 
Explanation: None