Answer:
The correct answer is B. When our chest cavity expands, air pressure in the lungs is reduced, causing air molecules to rush into the lungs.
Step-by-step explanation:
The thoracic cavity, or thorax, is an airtight box that houses the bronchial tree, lungs, heart and other structures. The ribs and the attached muscles form the upper and the sides of the thorax; The lower part is formed by a large muscle called a diaphragm. The thoracic walls form a protective box around the lungs and other contents of the thoracic cavity.
Breathing is the set of events that results in the exchange of oxygen from the environment and carbon dioxide from the body's cells. The process by which air enters the lungs is called inspiration, or inhalation, and the process of expulsion is called expiration, or exhalation.
When inspiring, the diaphragm moves down in the direction of the abdomen, and the rib muscles pull the latter up and out. In this way, the volume of the thoracic cavity increases. The air pressure in the thoracic cavity and lungs is reduced. As gases flow from high to low pressures, the air from the outside environment enters the lungs through the nose or mouth.
Then the correct answer is B. When our chest cavity expands, air pressure in the lungs is reduced, causing air molecules to rush into the lungs.