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: Dental
Function of the maxillary sinus is: 
Select and explain. 
A. Protects the skull against mechanical shock., B. Defence against bacterial infection., C. It warms and moistens the inspired air., D. All of the Above.
D: All of the Above.
Answer: D: All of the Above. 
Explanation: Functional Importance and Clinical Considerations
Many functions are attributed to maxillary sinus. Being an air space it lessens the weight of skull, gives resonance to the voice and protects the skull against mechanical shock. It warms and moistens the inspired air. The lysozyme it produces is bactericidal and thus contributes to the defense against bacterial infections.