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
Amalgam often tends to discolor the teeth. This can be inhibited by using: 
Select and explain. 
A. A zinc free alloy, B. An alloy containing zinc, C. Calcium hydroxide on the pulpal floor, D. Cavity varnish on all cut surfaces
D: Cavity varnish on all cut surfaces
Answer: D: Cavity varnish on all cut surfaces 
Explanation: None