What's the meaning of a pneumatic bones ?

The pneumatic bones are important to birds for respiration. They are hollow bones which are connected to the bird's respiratory system and are important for birds to be able to breath. Examples of pneumatic bones are the skull, humerus, clavicle, keel (sternum), pelvic girdle, and the lumbar and sacral vertebrae.

Ithink the answer is b
not sure

Geographic isolation.glad i could : )