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
Copal varnish is: 
Select and explain. 
A. ZnO resin, B. Ca(OH)2, C. ZnO glycerin, D. All of the above
A: ZnO resin
Answer: A: ZnO resin 
Explanation: None