Final answer:
The best projection to demonstrate lateral deviation of the nasal septum is the lateral projection, which provides a clear profile view of the septum's structure.
Step-by-step explanation:
The lateral deviation of the nasal septum may be best demonstrated in the A. lateral projection. The nasal septum is a flat, midline structure that divides the nasal cavity into two halves. It is formed by the perpendicular plate of the ethmoid bone, the vomer bone, and the septal cartilage. For demonstrating septal deviations, the lateral projection allows for a clear and profile view of the septum, showing any deviation from the midline.