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
[{'content': 'Longest part of optic nerve \nSelect and explain. \nA. Intraocular, B. Intracranial, C. Intraorbital, D. Intracranial', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The optic nerve is about 47- 50 mm in length and can be divided into 4 parts : \nintraocular (1mm), intraorbital (30mm), intracanalicular (6-9mm)and intracranial (10mm).', 'role': 'assistant'}]