Which one of the following prevents the collapsing of the trachea...

The trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of the 5th thoracic vertebra into a right and left primary bronchi. The trachea, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings. These C-shaped rings of hyaline cartilage provide structural support and prevent the trachea from collapsing even when there is no air in it.

Answer: Cartilagenous rings.