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: Medicine
Which of the following causes vasodilation in the pulmonary circulation? 
Select and explain. 
A. Hypercarbia, B. Hypoxia, C. PGE, D. PGI
D: PGI
Answer: D: PGI 
Explanation: Substances producing pulmonary vasodilation include nitric oxide, prostacyclins, a2 and b2 adrenergic stimulation, histamine etc. Hypercapnia, hypoxy endothelin I, a1 adrenergic, angiotensin II, thromboxane produce pulmonary vasoconstriction.