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 main advantage of composites over unfilled direct filling resin is their: \nSelect and explain. \nA. Higher solubility in saliva, B. Lower modulus of elasticity, C. Esthetic excellence, D. Lower thermal co-efficient of expansion', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]