Type I alveolar cells:

a. secrete surfactant.

b. are squamous epithelial cells.

c. are macrophages.

d. function mainly in the diffusion of gases.

e. Both B and D.

The correct option is: e. Both B and D

Explanation:

Type I alveolar cells are the thin squamous epithelial cells that lines the alveolar surface of the pulmonary alveoli.

These cells are involved in the gas exchange process. The thin lining of the type I alveolar cells, allows the rapid diffusion of gas and thus enabling the exchange of gases between the blood present in the capillaries and the air present in the pulmonary alveoli.