This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Anatomy
Concomitant administration of this drug with organic nitrates is contraindicated due to marked potentiation of vasodilatory action leading to profund hypotension. This drug is: 
Select and explain. 
A. Propanolol, B. Fluoxetine, C. Hydrochlorothiazide, D. Sildenafil
D: Sildenafil
Answer: D: Sildenafil 
Explanation: (Ref: KDT 6/e p525) Nitrates release No, that acts by increasing cGMP. Phosphodiesterase inhibitors like sildenafil inhibits the breakdown of cGMP. Concomitant use of these two drugs may result in profound hypotension.