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': 'Most radiosensitive phase of cell cycle is: \nSelect and explain. \nA. GI, B. G-2, C. S, D. M', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. M', 'role': 'assistant'}]