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
[{'content': 'Hardener in gypsum is \nSelect and explain. \nA. 2% K2SO4, B. Sodium sulphate, C. 4%K 2SO4, D. Nad', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]