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': 'Periodontitis is caused by \nSelect and explain. \nA. Malnutrition, B. Supra gingival plaque, C. Bio-film, D. Faulty tooth brushing', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]