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 preferred agent for base formation below restorative \nresin is: \nSelect and explain. \nA. Calcium hydroxide, B. Cavity varnish, C. Zinc oxide-eugenol cement, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]