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: Physiology
Pulmonary vasoconstriction is caused by 
Select and explain. 
A. Prostacyclin, B. Alpha-2 stimulation, C. Hypoxia, D. Histamine
C: Hypoxia
Answer: C: Hypoxia 
Explanation: Prostacyclin, alpha 2 stimulation, and Histamine are potent vasodilators.Ref: Ganong review of medical physiology 23rd edition Page no: 563