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 an alkylating agent? 
Select and explain. 
A. Chlorambucil, B. Ifosfamide, C. Nitrosurea, D. Cladrabine
D: Cladrabine
Answer: D: Cladrabine 
Explanation: Cladrabine REF: KDT ed p. 820 See APPENDIX-37 for "CLASSIFICATION OF CANCER CHEMOTHERAPY AGENTS"