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': 'Heat hardening is the process done at \nSelect and explain. \nA. Heating 750°C and slowly cooling to zero degrees, B. Heating quickly upto 450°C followed by sudden quenching, C. Heating upto 250°C for 15 to 30 min, D. Heating at 750° C and then quenching to room temperature', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]