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: Unknown
[{'content': 'All of the following are direct DNA interacting cytotoxic agents except \nSelect and explain. \nA. Melphalan, B. Hydroxyurea, C. Carmustine, D. Ifosfamide', 'role': 'user'}, {'content': 'Answer: B \nExplanation: All other agents are alkylating agents , whereas hydroxyurea is an anti metabolite acts at S phase of cell cycle indirectly affect DNA molecules.', 'role': 'assistant'}]