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
Function of space maintainers 
Select and explain. 
A. Prevent supra eruption of opposite tooth, B. Prevent migration of teeth, C. Maintain space, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None