Which of the following cause expiration

a) Relaxation of diaphragm muscles

b) Contraction of diaphragm muscles

c) Decrease in thoracic volume

d) Raising of ribs and sternum

e) Increase in intrapulmonary pressure

During expiration, relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and thereby the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs.