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': 'A young female patient reports to the dental office with complaint of small gaps between her teeth\n\nShade selection for such a treatment should be carried out under the \nSelect and explain. \nA. Natural day light, B. Fluorescent light, C. After placement of rubber dam, D. When the teeth are dry', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]