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': 'Plaster of paris: \nSelect and explain. \nA. Is wet calcined hemihydrate, B. Has porous and irregular crystals, C. Is α— hemihydrate, D. Has a W / P of 0.2', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]