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': 'Which of the following agent is not used for the treatment of erectile dysfunction? \nSelect and explain. \nA. PGE2, B. Vardenafil, C. Phenylephrine, D. Alprostadil', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]