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 thickness of the spacer used in special tray is \nSelect and explain. \nA. 2.5 mm, B. 2.0 mm, C. 1.5 mm, D. 1.0 mm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]