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': 'Which of the following is not a natural composite? \nSelect and explain. \nA. Enamel, B. Dentin, C. Hydroxyapatite crystals, D. None', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Composite literally meaning “made up of several parts or elements.”\nEnamel and dentine acts as composite structure.\xa0\nHydroxyapatite crystals acts as ﬁller.', 'role': 'assistant'}]