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': 'Gingival clefts may be caused by \nSelect and explain. \nA. Occlusal disharmonies, B. Faulty toothbrushing, C. Normal frenum attachment, D. Use of dental floss', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]