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 alkylating agent? 
Select and explain. 
A. Chlorambucil, B. Ifosfamide, C. Nitrosurea, D. Cladrabine
D: Cladrabine
Answer: D: Cladrabine 
Explanation: Ans. is 'd' i.e., Cladrabine