This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
[{'content': 'Hypoxic pulmonary vasoconstriction due to \nSelect and explain. \nA. Irreversible pulmonary vasocontriction hypoxia, B. Reversible pulmonary vasoconstriction due to hypoxia, C. Direct blood to poorly ventilated areas, D. Occurs hours after pulmonary vasoconstriction', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hypoxic pulmonary vasoconstriction (HPV), also known as the Euler-Liljestrand mechanism, is a physiological phenomenon in which small pulmonary aeries constrict in the presence of alveolar hypoxia (low oxygen levels). Ref Harrison20th edition pg 2334', 'role': 'assistant'}]