Final answer:
As the molecule moves into the airways, the diameter of the airways get progressively smaller and the total cross-sectional surface area of the airways decreases.
Step-by-step explanation:
As the molecule moves into the airways, the diameter of the airways get progressively smaller and the total cross-sectional surface area of the airways decreases. This is because the airways branch out into smaller and narrower passages, leading to a decrease in the overall surface area.