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
The role of sodium metabisulfite in Local anesthetic agent is: 
Select and explain. 
A. Preservative, B. Fungicide, C. Reducing agent, D. Vaso constrictor
C: Reducing agent
Answer: C: Reducing agent 
Explanation: None