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': 'Bruxism is mainly due to \nSelect and explain. \nA. Psychological stress, B. Diabetes, C. Functional grinding of teeth, D. None of above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]