The correct answer is dome-shaped.Breathing involves two stages: inspiration during which atmospheric air is drawn in and expiration by which the alveolar air is released out.During the inspiration, the diaphragm flattens and the chest cavity enlarges. This contraction creates a vacuum, which pulls air into the lungs.During the expiration, the diaphragm relaxes and returns to its domelike shape, and the air is forced out of the lungs.