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': 'A rough / chalky surface of the cast is due to all of the following except: \nSelect and explain. \nA. Not waiting for 20 min before pouring, B. Excess wetting agent left on impression, C. Air incorporation in the mix, D. Improper powder/water ratio of stone', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Air incorporation in the mix leads to bubbles.', 'role': 'assistant'}]