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': 'Effective dose in radiation at 2 m, is 1 gray ; At 1 m, it will be \nSelect and explain. \nA. 0.25, B. 0.5, C. 2, D. 4', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]