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: Anatomy
ARDS is due to a defect in: 
Select and explain. 
A. Type I pnemocytes, B. Type2 pnemocytes, C. Clara cells, D. Endothelial cells
D: Endothelial cells
Answer: D: Endothelial cells 
Explanation: ARDS is intiated by injury of pnemocytes and pulmonary endothelium setting in motion a viscious cycle of increasing inflammation and pulmonary damage.(ref Robbins 9th/672)