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
Most of the manufacturers supply the gold foil coated with_____. 
Select and explain. 
A. Aluminium chloride, B. Ammonium chloride, C. Both, D. None
B: Ammonium chloride
Answer: B: Ammonium chloride 
Explanation: It is coated in order to prevent contamination.