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 tobacco preparation mainly used to clean the tooth is: \nSelect and explain. \nA. Khaini, B. Mawa, C. Masheri, D. Dhumti', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Mishri/Masheri :\n\nIt is prepared by roasting tobacco on a hot metal plate until it is uniformly black. It is then powdered, it is used with or without catechu.\xa0\nCatechu is a residual extract obtained by soaking the heartwood of the tree Acacia Catechu or Acacia Suma in boiling water.\xa0\nIt is used primarily to clean teeth.\n\nSoben Peter\xa0\nEssentials of preventive and community dentistry\xa0\n4th edition', 'role': 'assistant'}]