Final answer:
The trachea divides into the right and left bronchi as it enters the lungs, which continue to split into smaller bronchioles leading to alveoli for gas exchange.
Step-by-step explanation:
The trachea branches into the right and left bronchi as it enters the lungs. The correct answer to the question is: a) Bronchi. The bronchi themselves continue to branch into smaller bronchioles within each lung, and these bronchioles lead to the alveoli where the gas exchange occurs. As air moves down from the trachea to enter the lungs, it is directed through these primary bronchi which then continue branching out, demonstrating the treelike structure of the respiratory system's airways.