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
[{'content': 'Dry ice is \nSelect and explain. \nA. Frozen CO2, B. 1,1,2,2 tetra fluoro ethylene, C. Ethyl fluoride, D. DichLoroDifluoro methane', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]