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Dear Student,

1. Three
2. Cartilaginous Rings- The cartilaginous rings cover the trachea to prevent from getting collapsed.
3. Alveoli- Alveoli are tiny balloon-like structures present inside our lungs. They are thin walled. They have large surface area in relation to the volume. They are lined by a fluid which enables the gases to dissolve easily. They contain an extensive network of blood capillaries. This structure of alveoli allows exchange of O and CO between the blood of the capillaries that surround the alveoli and the gases present in the alveoli.


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