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
[{'content': 'Amalgam often tends to discolor the teeth. This can be inhibited by using: \nSelect and explain. \nA. A zinc free alloy, B. An alloy containing zinc, C. Calcium hydroxide on the pulpal floor, D. Cavity varnish on all cut surfaces', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]