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
Sodium–nitroprusside acts by activation of: 
Select and explain. 
A. Guanylate cyclase, B. K+ channels, C. Ca++ channels, D. Cyclic AMP
A: Guanylate cyclase
Answer: A: Guanylate cyclase 
Explanation: Nitroprusside generates NO that relaxes vascular smooth muscles by activating guanylate cyclase.