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': 'Powders of dental plaster and dental stone differ\nmainly in: \nSelect and explain. \nA. Solubility, B. Shelf life, C. Chemical formula, D. Particle porosity', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]