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': "The technique of blocking the facial nerve at the neck of mandible is: \nSelect and explain. \nA. Van Lint's block, B. O'Brien's block, C. Nadbath block, D. Atkinson's block", 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. O'Brien's block", 'role': 'assistant'}]