Explanation

Cartilaginous rings in the respiratory tract, like those in the trachea and bronchi, serve multiple functions: 

Support:

The rings provide structural support to the airways.

They keep the trachea and bronchi open and stable. 

Keep the passage open:

This is directly related to the support function.

Prevent collapsing:

The rings are crucial in preventing the collapse of the airways, especially during exhalation when pressure changes occur.