Final answer:
Pulmonary ventilation involves inspiration and expiration, with inspiration causing air to enter the lungs and expiration causing air to leave the lungs. The correct option is c.
Step-by-step explanation:
Pulmonary ventilation comprises two major steps: inspiration and expiration. Inspiration is the process that causes air to enter the lungs, and expiration is the process that causes air to leave the lungs.
A respiratory cycle is one sequence of inspiration and expiration. The muscles involved in inspiration include the diaphragm and the external intercostal muscles.
When the diaphragm contracts and the external intercostal muscles move the ribs upward and outward, the thoracic cavity expands, creating a pressure lower than atmospheric pressure and driving air into the lungs. Option c. is the correct one.