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
At higher concentration flouride is bactericidal, because: 
Select and explain. 
A. It's action on bacterial enzymes., B. It coagulates the bacterial proteins., C. It destroy the bacterial cell wall, D. All of the above.
A: It's action on bacterial enzymes.
Answer: A: It's action on bacterial enzymes. 
Explanation: At higher concentrations, fluoride is bactericidal, because of its action on two bacterial enzymes enolase and phosphoglucomutase.