Question

which airways contain smooth muscle in their walls and no cartilage, making them able to constrict and dilate?
main bronchi
segmental bronchi
alveoli
bronchioles

Explanation:

Main bronchi and segmental bronchi have cartilage in their walls. Alveoli are tiny air - sacs without smooth muscle for constriction/dilation. Bronchioles have smooth muscle in their walls and lack cartilage, allowing them to constrict and dilate.

Answer:

Bronchioles