What is the function of the part that is labeled A?
The parts of the upper respiratory tract are labeled. Part A is the sinuses.
moistens and filters incoming air
prevents food and liquid from entering
vibrates and produces sound
exchanges oxygen and carbon dioxide

The main function of sinuses is they produces a mucus that moistens and filters the incoming air.

Explanation:

The sinus cavities are found in the cranial bone that helps to filter and moisture the air that is inhaled through nasal passages and also they will remove the unwanted particles .

The functions of sinuses are to make skull lighten and they help to produce sound by giving effects to voice and they produce mucus to provide lubrication. It is a part of the respiratory tract. There are four paranasal sinuses they are maxillary, ethmoid, sphenoid and frontal.

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