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 best method for radiation protection of the operator? \nSelect and explain. \nA. Standing behind a lead barrier, B. Wearing a lead apron, C. Following the "position and distance" rule, D. Standing 6 feet away from the X-ray tube during exposure', 'role': 'user'}, {'content': "Answer: A \nExplanation: Operators of radiographic equipment should use barrier protection when possible, and barriers should contain a leaded glass window to enable the operator to view the patient during exposure. When shielding is not possible, the operator should stand at least two meters from the tube head and out of the path of the primary beam (ADA 2006).\n\xa0\nWhite and Pharoah's Oral\xa0 Radiology Principles and Interpretation 8th edition", 'role': 'assistant'}]