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': 'The zinc oxide-eugenol impression pastes harden by: \nSelect and explain. \nA. Chemical reaction, B. Cold, C. Heat, D. Pressure', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Key Concept:\xa0 ZnO Eugenol impression paste hardens by chemical reaction.', 'role': 'assistant'}]