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
Porcelain bonded to metal is strong when it is 
Select and explain. 
A. Air fired, B. Tempered after firing, C. Fired under compression, D. Fired several times before completion
B: Tempered after firing
Answer: B: Tempered after firing 
Explanation: None