This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General surgery, Subject name: Surgery
[{'content': 'Posterior triangle lymph nodes are \nSelect and explain. \nA. Level 4, B. Level 5, C. Level 6, D. Level 7', 'role': 'user'}, {'content': 'Answer: B \nExplanation: ISub mandibulaeIIUpper deep cervicalIIIMid-cervicalIVLower cervicalVPosterior triangleVIPre laryngeal/pre trachealVIIMediastinalRef: Bailey and love pg: 764', 'role': 'assistant'}]