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: Unknown
[{'content': 'Length of intraorbital part of optic nerve is : \nSelect and explain. \nA. 10-12 mm, B. 20-24 mm, C. 25-30 mm, D. 35-40 mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Length of optic nerve – 5 cm\n\nIntraocular portion – 20 mm\nIntraorbital portion – 30 mm', 'role': 'assistant'}]