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
Fluoride in any form is contraindicated in: 
Select and explain. 
A. Chronic renal failure, B. Osteoporosis, C. Hypertension, D. Thyrotoxicosis
A: Chronic renal failure
Answer: A: Chronic renal failure 
Explanation: None