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': 'Sublimation is the conversion of a: \nSelect and explain. \nA. Solid directly to gas, B. Gas to liquid and then to solid, C. Gas directly to liquid, D. Solid to liquid and then to gas', 'role': 'user'}, {'content': 'Answer: A \nExplanation: It is possible for some solids to change directly to a vapor by a process called sublimation as seen in dry ice; this, however, has no practical importance as far as dental materials are concerned.\nSublimation is the conversion of a solid directly to gas.\nReference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 18', 'role': 'assistant'}]