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 an alkylating agent? 
Select and explain. 
A. Cyclophosphamide, B. Busulfan, C. 5-Fluorouracil, D. Melphalan
C: 5-Fluorouracil
Answer: C: 5-Fluorouracil 
Explanation: 5- Fluorouracil' Repeat from AI1MS 09