This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Pharmacology
[{'content': 'Which of the following drug used in the Management of Pulmonary Hypeension acts by inhibiting Phosphodiesterase enzyme? \nSelect and explain. \nA. Epoprostenol, B. Bosentan, C. Nifedipine, D. Sildenafil', 'role': 'user'}, {'content': 'Answer: D \nExplanation: First line drugs for Functional class II-III PAH : cGMP Signaling Modulators: PDE-5 Inhibitors - Sildenafil, Tadalafil, Vardenafil cGMP Signaling Modulators: sGC Stimulator - Riociguat Endothelin Receptor Antagonists - Bosentan, Ambrisentan First line drugs for Functional class IV PAH: IP Receptor Agonists: Prostacyclin and Prostacyclin Analogs - Epoprostenol, Selexipag . L-type Ca2+ Channel Blockers like Nifedipine, Amlodipine: Use only in PAH patients with positive vasodilator testing.', 'role': 'assistant'}]