A.
<u>The ribcage expands to allow air to enter the lungs</u> is an example of the skeletal system interacting directly with the respiratory system.
Explanation:
The skeletal system is mainly made up of bones - like the ribcage in this case - while the respiratory system is made up of the lungs, trachea, diaphragm, etc.
When inhaling, the diaphragm contracts, therefore increasing the volume of the chest cavity. The muscles between the ribs also contract causing the ribcage to stretch upwards and outwards. This also contributes to an increase in the volume of chest cavity. Consequently, the pressure in the chest, decreases causing atmospheric pressure to rush air into the lungs.
When these muscles contract, they raise the pressure in the chest cavity causing air to rush out of the lungs.
Learn More:
For more on interaction of the skeletal system and the respiratory system check out;
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