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: Pharmacology
[{'content': 'Which of the following is not used in the treatment of pulmonary hypertension ? \nSelect and explain. \nA. Calcium channel blockers, B. Alpha blockers, C. Prostacyclins, D. Endothelin receptor antagonists', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]