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': 'Calculus is detrimental to the gingival tissues because it is \nSelect and explain. \nA. A mechanical irritant, B. Covered with bacterial plaque, C. Composed of calcium and phosphorous, D. Locked into surface irregularities', 'role': 'user'}, {'content': 'Answer: B \nExplanation: calculus is calcified dental plaque. It is always covered by a layer of uncalcified plaque, which is detrimental to the gingival tissues.', 'role': 'assistant'}]