Air moves out of the lungs when the
(a) diaphragm relaxes and the rib cage moves inward.
(b) air pressure inside the lungs is less than the external air pressure.
(c) diaphragm contracts and the rib cage expands.
(d) air pressure inside the lungs is the same as the external air pressure.
The diaphragm relaxes, and the dome moves upwards. As for the ribs, they move upwards and outwards in inspiration, again to increase the volume of the chest cavity, and downwards and inwards in expiration.
