The answer to this is C. Sodium fluoride is known to be effective as a preservative of blood glucose. For those who are unaware, sodium fluoride is known to be an inorganic compound. The formula for this is NaF. This usually comes in solid form but you can place it in water and it will be soluble.
This is often used in order to prevent cavities from causing some chaos to the teeth. There are still some studies that are being done in order to see if this would not cause any issues with the teeth in the long run. Some pharmaceutical products contain this as one of the ingredients.