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
Hardener in gypsum is 
Select and explain. 
A. 2% K2SO4, B. Sodium sulphate, C. 4%K 2SO4, D. Nad
A: 2% K2SO4
Answer: A: 2% K2SO4 
Explanation: None