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 is NOT a prodrug ? 
Select and explain. 
A. Enalapril, B. Imipramine, C. Sulphasalazine, D. Cyclophosphamide
B: Imipramine
Answer: B: Imipramine 
Explanation: None