There are exactly three recycling centers in Rivertown: Center 1, Center 2, and Center 3. Exactly five kinds of material are recycled at these recycling centers: glass, newsprint, plastic, tin, and wood. Each recycling center recycles at least two but no more than three of these kinds of material. The following conditions must hold: Any recycling center that recycles wood also recycles newsprint. Every kind of material that Center 2 recycles is also recycled at Center 1. Only one of the recycling centers recycles plastic, and that recycling center does not recycle glass. 21. If each recycling center in Rivertown recycles exactly three kinds of material, then which one of the following could be true?