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: Surgery
[{'content': 'The role of sodium metabisulfite in Local anesthetic agent is: \nSelect and explain. \nA. Preservative, B. Fungicide, C. Reducing agent, D. Vaso constrictor', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]