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
Best space maintainer is: 
Select and explain. 
A. Active space maintainer, B. Passive space maintainer, C. Band and loop, D. Pulpotomised primary tooth
D: Pulpotomised primary tooth
Answer: D: Pulpotomised primary tooth 
Explanation: None