Final answer:
The bone that forms the inferior part of the nasal septum is marked by the letter C, representing the vomer bone.
Step-by-step explanation:
The letter that indicates the bone that forms the inferior part of the nasal septum is C, which represents the vomer bone. The vomer is an unpaired, triangular-shaped bone that forms the posterior-inferior part of the nasal septum. The superior portion of the nasal septum is formed by the perpendicular plate of the ethmoid bone, and together, these structures separate the left and right nasal cavities providing support and passage for inhaled air.