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
The thickness of the spacer used in special tray is 
Select and explain. 
A. 2.5 mm, B. 2.0 mm, C. 1.5 mm, D. 1.0 mm
B: 2.0 mm
Answer: B: 2.0 mm 
Explanation: None