Concept:Contraction of the intercostal muscles is a key step in the mechanism of breathing in mammals.
Explanation:The intercostal muscles are located between the ribs.
When these muscles contract, they pull the ribs upward and outward.
This movement is known as the process described in statement I.
As the ribs move upward and outward, the size of the rib cage increases.
This causes the thoracic cavity to expand, and the volume inside the chest increases.
An increase in volume lowers the air pressure inside the thoracic cavity.
Since the outside atmospheric pressure is now higher, air rushes into the lungs.
Thus, the contraction of the intercostal muscles directly causes the ribs to move upward and outward.
This is an important part of inhalation or inspiration.
Answer:The correct answer is A. I.