The main function of the respiratory system is to O pump wastes.
O exchange O2 and CO2 gases.
filter wastes.
O transport O2 and CO2 gases.

exchange O2 and CO2 gases.

Explanation:

The respiratory system's main function is to exchange oxygen and carbon dioxide gases within the body. The organs that make up the respiratory system include the nose, pharynx and larynx, the trachea, bronchi, and the lungs. Each of these organs help with the process of breathing and/or the exchanging of gases within them.

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when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

the missing space is phylum