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: Dental
[{'content': 'The superior border of lingual bar should lie \nSelect and explain. \nA. Deep in the lingual sulcus, B. At least 4 mm below the gingival margin, C. At the cingutum of anterior teeth, D. At least 7 mm below the gingival margin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]