Like the kidneys,the lungs demonstrate functional unity; that is,each unit is structurally and functionally identical.The basic physiological unit of the lung is the respiratory unit,which consists of:

A)Nonrespiratory and respiratory bronchioles,alveolar ducts,and alveolar sacs.
B)Respiratory bronchioles,alveolar ducts,and alveolar sacs.
C)Bronchi,nonrespiratory bronchioles,and respiratory bronchioles.
D)Conducting airways,alveolar ducts,and alveolar sacs.