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: Radiology
[{'content': 'The most sensitive cell cycle stage for radiotherapy is: \nSelect and explain. \nA. S phase, B. G1, C. G2, D. G2M', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. G2M', 'role': 'assistant'}]