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
Agents used for cold test: 
Select and explain. 
A. Dichloro difluromethane., B. Dry ice., C. Ethylchloride., D. All of the above.
D: All of the above.
Answer: D: All of the above. 
Explanation: None