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
[{'content': 'Which of the following has LEAST chance of progression in multiple sclerosis? \nSelect and explain. \nA. Optic nerve involvement, B. Absence of oligoclonal band in CSF, C. Transverse myelitis, D. Pyramidal tract involvement', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]