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': 'Porcelain bonded to metal is strong when it is \nSelect and explain. \nA. Air fired, B. Tempered after firing, C. Fired under compression, D. Fired several times before completion', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]