What respiratory tubes found in the lungs are lined with epithelial tissue and held open by varying amounts of cartilage?

The respiratory tubes in the lungs that are lined with epithelial tissue and held open by varying amounts of cartilage are the bronchi and the bronchioles. The bronchi are the larger respiratory tubes that branch off the trachea and enter the lungs, while the bronchioles are the smaller respiratory tubes that branch off the bronchi and lead to the alveoli.