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
What is the length of optic nerve 
Select and explain. 
A. 20 mm, B. 30 mm, C. 40 mm, D. 50 mm
D: 50 mm
Answer: D: 50 mm 
Explanation: Answer- D. 50 mmoptic nerve is about 47-50 mm in length and can be divided into 4 pas : -Intraocular pa (1 mm)Intraorbital pa (30 mm)Intracanalicular pa (5-9 mm)Intracranial pa (10 mm)