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
Which is the earliest feature of multiple sclerosis ? 
Select and explain. 
A. Internuclear opthalmoplegia, B. Optic neuritis, C. Cerebellar ataxia, D. Diplopia
B: Optic neuritis
Answer: B: Optic neuritis 
Explanation: Sudden onset of optic or retrobulbar optic neuritis without any associated CNS involvement can be interpreted as the first sign or only sign of multiple sclerosis provided other causes of optic neuritis are excluded. Reference: Current Medical Diagnosis and Treatment By Panda 3rd edition page 537.