Because it is asking for a teaching technique don't think that an x-ray would show Amanda her plaque. A dentrifice is a polishing solution used for after a teeth cleaning, that would not show Amanda her plaque. A normal mouth wash would not show Amanda her plaque.
The only answer that would show Amanda where her plaque is is a disclosing solution! They even sell it for kids as mouth wash so they can make sure they get all the plaque off when they brush.
So C. a disclosing solution is the answer.
