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': 'Cause of expansion in Zinc containing amalgam is: \nSelect and explain. \nA. Zinc + water, B. Water, C. Hydrogen, D. Nascent oxygen', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]