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
The porcelain-metal bond is 
Select and explain. 
A. Chemical, B. Mechanical, C. 1 and 2, D. None of the above
C: 1 and 2
Answer: C: 1 and 2 
Explanation: None