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
In doing gingival retraction, all of the following are used except 
Select and explain. 
A. 8% racemic epinephrine, B. 8% alum, C. 8% zinc chloride, D. 40% zinc chloride
D: 40% zinc chloride
Answer: D: 40% zinc chloride 
Explanation: None