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: Radiology
Hardener among the following is: 
Select and explain. 
A. Sodium sulfite, B. Ammonium sulfite, C. Aluminium salts, D. None of the above
C: Aluminium salts
Answer: C: Aluminium salts 
Explanation: None