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: Medicine
With regard to sickle cell disease - 
Select and explain. 
A. 25% of the black population have sickle cell disease, B. The most severe form of sickle cell retinopathy is associated with SS disease, C. Optic disc is the first site of neovascularization in patient with severe retinal ischamia, D. None of the above
D: None of the above
Answer: D: None of the above 
Explanation: None