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': 'Impurities in casting is removed by: \nSelect and explain. \nA. Annealing, B. Degassing, C. Pickling, D. Conditioning', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]