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': 'Fiber-optic trans-illumination (FM) method of caries\ndiagnosis is based on the principle of: \nSelect and explain. \nA. When Laser beam falls on carious enamel, it gives a bluish hue., B. A fluorescent dye is taken up by carious dentine which can be viewed easily, C. There\tis\ta\tdifferent index\tof\tlight\ttransmission\tfor decayed or sound enamel., D. The conductance of normal and decayed tooth tissue is different.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]