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': 'Which of the following is the most radio sensitive phase of the cell cycle? \nSelect and explain. \nA. G2M, B. G2, C. S, D. G1', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Studies on synchronously dividing cells in culture have revealed greatest radio sensitivity for cells in G2 and M phase, and relative radio resistance for cells in late S phase, and intermediate radio sensitivity between these two extremes. Ref: Progress In Cell Cycle Research By Laurent Meijer, Armelle Jezequel,Lernard Ducommun, Volume 4, Page 202; Basic Radiation Oncology By Beyzadeoglu, Murat Beyzadeoglu, Gokhan Ozyigit, Cuneyt Ebruli, Pages 75-77', 'role': 'assistant'}]