This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Unknown
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 part of the blood-air barrier.