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
Lethal dose of fluoride is: 
Select and explain. 
A. 250 milligrams, B. 500 milligrams, C. 5 grams, D. 10 grams
C: 5 grams
Answer: C: 5 grams 
Explanation: None