This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
[{'content': 'Thickness of lead apron to prevent radiation - \nSelect and explain. \nA. 1 mm, B. 3 mm, C. 0.5mm, D. 7mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: lead aprons of thickness 0.5mm will reduce the intensity of scattered X rays over 90% and should be worn by all workers regularly exposed to X ray procedures. Radiation protection is the youngest bramch of hygiene and is called radiation hygiene. Parks textbook of preventive and social medicine.K Park. Edition 23.page no: 745', 'role': 'assistant'}]