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
Advantages of rubber dam are 
Select and explain. 
A. a dry,clean operating field,, B. improved access and visibility,, C. potentially improved properties of dental materials,, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: A dry, clean operating field,
Improved access and visibility,
Potentially improved properties of dental materials,
Protection of the patient and operator, and
Operating efficiency.