As a Molecule of Oxygen Passes from Alveolar Air into the Blood

Multiple Choice

As a molecule of oxygen passes from alveolar air into the blood it passes through the layers of the respiratory membrane in what order?
1) epithelial basement membrane
2) capillary basement membrane
3) alveolar epithelial wall
4) capillary endothelial wall

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