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
[{'content': 'Which of the following is an alkylating agent? \nSelect and explain. \nA. Chlorambucil, B. Ifosfamide, C. Nitrosurea, D. Cladrabine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Cladrabine REF: KDT ed p. 820 See APPENDIX-37 for "CLASSIFICATION OF CANCER CHEMOTHERAPY AGENTS"', 'role': 'assistant'}]