The correct answer is - When it contracts, it compresses the thorax and decreases its volume.
Explanation:
The diaphragm is a skin muscle that separates the stomach and chest and fits at the base of the chest and covers the lungs and thoracic cavity. The prime mover is the diaphragm as it is responsible for the major muscle during inhalation.
It flattens during inspiration by contracts and increases the chest cavity or thoracic cavity and increases the volume of the thorax and diminishes the pressure inside the lungs and air gets in the lungs.
