Answer:

Introduction:
The respiratory tree consists of the airways that transport air from the nose and mouth to the lungs. It is made up of several structures, including the trachea, bronchi, bronchioles, and alveoli.

Explanation:
Out of the given options, the structure that is not a part of the respiratory tree is B) atria. Atria are the upper chambers of the heart that receive blood from the veins and pump it into the ventricles. They have no role in the respiratory system.

The other structures mentioned in the options are as follows:

A) Alveolar duct: It is a small tube that connects the respiratory bronchioles to the alveolar sacs. It is the site where gas exchange takes place between the lungs and the bloodstream.

C) Segmental bronchi: These are the primary bronchi that branch off from the trachea and supply air to the different segments of the lungs.

D) Respiratory bronchiole: It is a thin-walled tube that branches off from the terminal bronchioles and contains alveoli in its walls. It is the site where gas exchange occurs in the lungs.

Conclusion:
In conclusion, the atria is not a part of the respiratory tree, while the alveolar duct, segmental bronchi, and respiratory bronchiole are all essential structures that make up the respiratory system.

Primary bronchi branched give rise to 2dary bronchi that lead tertiary bronchiole all are formed respiratory tree part so Atria is the correct answer