This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Pathology
The blood-air barrier consists of all of the following Except 
Select and explain. 
A. Alveolar pores, B. A layer of surfactant, C. Type I alveolar cell cytoplasm, D. Fused basal lamina of alveolar and endothelial cells
A: Alveolar pores
Answer: A: Alveolar pores 
Explanation: Alveolar pores connect neighboring alveoli and function in equalizing pressure in the alveoli and enable collateral circulation of air. They do not constitute pa of the blood-air barrier.