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: Skin
Wavelength of UVB is : 
Select and explain. 
A. 250-280 nm, B. 280-320 nm, C. 320-400 nm, D. 400-700 nm
B: 280-320 nm
Answer: B: 280-320 nm 
Explanation: Ans. B. 280-320 nmThe wavelength found most effective in treating skin disease with phototherapy is UVB with warden gfh of 311 (+- 2nm) (narrow band UVB, NBUVB).The wavelengths between 4(N and 7AO nm are visible to the human eye.