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
Chemical method of strengthening porcelain
involves 
Select and explain. 
A. exchange of aluminium and sodium ions, B. exchange aluminium and potassium ions, C. exchange of sodium and potassium ions, D. none of the above
C: exchange of sodium and potassium ions
Answer: C: exchange of sodium and potassium ions 
Explanation: None