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': 'Sodium–nitroprusside acts by activation of: \nSelect and explain. \nA. Guanylate cyclase, B. K+ channels, C. Ca++ channels, D. Cyclic AMP', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Nitroprusside generates NO that relaxes vascular smooth muscles by activating guanylate cyclase.', 'role': 'assistant'}]