I chose a plastic toy, but the correct answer was newspaper.
Acid makes newspaper decay and fall apart rapidly.
When newspaper touches other materials, such as cloth, metal, or other paper, the acids will also attack these things and make them decay faster. Newspaper, most paperback books, newsprint, cheap drawing paper, construction pape, tissue paper, giftwrap - all these are made from woodpulp that will quickly crumble and decay. If you are planning to put any paper in a time capsule, be sure it is acid-free. Save the past for the future and make your own Millennium time capsule.