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
Most common cause of optic neuritis 
Select and explain. 
A. Ethyl alchol, B. Anterior ischeamic optic neuropathy, C. Leber's disease, D. Multiple sclerosis
D: Multiple sclerosis
Answer: D: Multiple sclerosis 
Explanation: M/C cause - Multiple sclerosis, Vit B12 deficiency, B2 deficiency.