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': 'In amalgam alloy which acts as oxygen scavenger: \nSelect and explain. \nA. Cu, B. Zn, C. Pd, D. Ag', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]