| 摘要 |
A teaching aid has a book with the pages secured by a spiral binding to flip over one by one. The sheets are in pairs with the top sheet having a window through which questions can be accessed on the second sheet. The corresponding answers on the second sheet are covered by the first sheet. The user simply works through the questions and subsequently checks the answers. Additional questions and answers can be printed on the reverse sides of the pages, increasing the application of the book.
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