Which of the following statements is correct?
- AAlveoli have goblet cells to produce mucus to trap pathogens from the air.
- BCartilage in the bronchi keeps the bronchi open and allows air to flow through freely.
- CComplete rings of cartilage in the bronchioles make sure that air can reach the alveoli.
- DDuring exercise, muscles in the bronchioles and alveoli relax to allow a greater flow of air.