37Gas ExchangeMedium1 markWhich statement correctly describes a structure of the human gas exchange system?AThe wall of an alveolus is only one cell thick and contains smooth muscle to allow contraction and expansion.BThe wall of a bronchiole consists of a thin layer of cartilage and a thin layer of smooth muscle.CThe wall of a bronchus has a folded inner layer of ciliated epithelium, which contains many goblet cells.DThe wall of the trachea contains many ciliated epithelial cells and is supported with complete rings of cartilage.Grade answerGrading criteria