This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of health and disease, Subject name: Social & Preventive Medicine
A sunscreen ointment has a Sun-Protection-Factor (SPF) of 15.How much of UV radiation it filters out. 
Select and explain. 
A. 15%, B. 85%, C. 93%, D. 98%
C: 93%
Answer: C: 93% 
Explanation: "SPF 15" means that 1/15th of the burning radiation reaches the skin through the recommended thickness of sunscreen SPF 15 sunscreens filter out about 93% of UVB rays, while SPF 30 sunscreens filter out about 97%, SPF 50 sunscreens about 98% Ref: https://en.m.wikipedia.org/wiki/Sunscreen