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': 'For strength and rigidity, the vertical height of a finished\nlingual bar should be at least \nSelect and explain. \nA. 6mm, B. 7mm, C. 4mm, D. 5mm', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]