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
Concomitant administration of this drug with organic nitrates is contraindicated due to marked potentiation of vasodilatory action leading to profound hypotension. This drug is: 
Select and explain. 
A. Propranolol, B. Fluoxetine, C. Hydrochlorothiazide, D. Sildenafil
D: Sildenafil
Answer: D: Sildenafil 
Explanation: None