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: Social & Preventive Medicine
[{'content': 'Thickness of lead apron to prevent radiation – \nSelect and explain. \nA. 1mm, B. 3mm, C. 0.5mm, D. 7mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Lead aprons (0.5mm of lead) will reduce the intensity of scattered X-ray over 90% and should be worn by all workers regularIy associated with x-ray procedures.', 'role': 'assistant'}]