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
[{'content': 'All are causes of pulmonary hypertension except- \nSelect and explain. \nA. Hyperventilation, B. Morbid obesity, C. High altitude, D. Fenfluramine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]