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: Ophthalmology
Normal Cup : disc ratio of optic disc is 
Select and explain. 
A. 0.3 to 0.4, B. 0.2 to 0.3, C. 0.5 to 0.6, D. 0.1 to 0.3
A: 0.3 to 0.4
Answer: A: 0.3 to 0.4 
Explanation: Normal Cup : disc ratio of optic disc 0.3 to 0.4.