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
Powders of dental plaster and dental stone differ
mainly in: 
Select and explain. 
A. Solubility, B. Shelf life, C. Chemical formula, D. Particle porosity
D: Particle porosity
Answer: D: Particle porosity 
Explanation: None