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': 'In "Thylstrup Fejereskov Index", \'Opaque white lines are more pronounced and frequently merge to form small cloudy areas scattered over the whole surface area\', the score given is \nSelect and explain. \nA. 2, B. 4, C. 6, D. 7', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]