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': 'Retrobulbar injection of xylocaine blocks all of the following except: \nSelect and explain. \nA. 3rd cranial nerve, B. 4th cranial nerve, C. 6th cranial nerve, D. Ciliary nerves and ciliary ganglion', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. 4th cranial nerve', 'role': 'assistant'}]