# The natural drainage of maxillary air sinus is impeded because:
A. Its opening into the middle meatus is narrow
B. Of its large size
C. Placement of its opening is higher than its floor
D. Its base is directed towards the lateral wall of the nasal cavity
The correct answer is C. Placement of its opening is higher than its floor.
The maxillary sinus is the one most commonly involved in infection of nasal cavity. This is probably because its aperture is located superior to its floor, impeding its natural drainage.
