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': "'Crippling Fluorosis' is characterized by: \nSelect and explain. \nA. Blockage of blood vessels, B. Chipping of teeth, C. Rigid spine, D. Calcification of blood vessels", 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]