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': 'Cells are most sensitive to radiation in: \nSelect and explain. \nA. G2 phase, B. G1 phase, C. G1 phase and early S phase, D. G2 phase and late S phase', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]