Which row correctly describes the human gas exchange system?
- Acartilage: trachea present, bronchus present, alveolus absent
- Bciliated epithelium: trachea absent, bronchus present, alveolus absent
- Cgoblet cells: trachea present, bronchus absent, alveolus absent
- Dsmooth muscle: trachea present, bronchus present, alveolus present