This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Air, Light, Sound, Housing, Radiation, Waste Disposal, Subject name: Social & Preventive Medicine
Lead aprons of ___ mm will reduce the intensity of scattered X -rays over ____ per cent and should be worn by all workers regularly associated with X-ray procedures. 
Select and explain. 
A. 0.2 and 60, B. 0.3 and 70, C. 0.4 and 80, D. 0.5 and 90
D: 0.5 and 90
Answer: D: 0.5 and 90 
Explanation: Lead aprons of 0.5 mm will reduce the intensity of scattered X -rays over 90 per cent and should be worn by all workers regularly associated with X-ray procedures.