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 periodontium remains healthier when crown margins \nare placed \nSelect and explain. \nA. At the gingival crest, B. Above the gingival margin, C. About 1/2 mm apical to the gingival crest, D. About 1 mm apical to the gingival crest', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]