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': 'Palladium is added to polyvinyl siloxane to \nSelect and explain. \nA. Act as a scavenger, B. Helps as surfactant, C. Acts as plasticizer, D. Acts as a catalyst', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]