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
Which of the following agent is not used for the treatment of erectile dysfunction? 
Select and explain. 
A. PGE2, B. Vardenafil, C. Phenylephrine, D. Alprostadil
C: Phenylephrine
Answer: C: Phenylephrine 
Explanation: None