The Lining of the Lower Respiratory Tract Presents Barriers to Drug

The lining of the lower respiratory tract presents barriers to drug absorption and includes which of the following elements?
1) Airway surface liquid
2) Capillary vascular network
3) Epithelial cells
4) Interstitium

A) 1 and 2 only
B) 1 and 3 only
C) 1,2,and 3 only
D) 1,2,3,and 4