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': 'Titanium casting is done: \nSelect and explain. \nA. Under vacuum in argon atmosphere, B. Under air pressure in nitrogen atmosphere, C. In specially fabricated aluminum vanadium crucibles, D. Using CAD-CAM technique', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]