(2021•山东) 阅读短文，在空白处填入适当的内容或括号内单词的正确形式。
Paper-making is one of the four great ancient Chinese inventions. Paper can be 1 (use) by people in many ways. We 2 (usual) use paper to make newspapers， magazines and books. The famers 3 live in Finland even wear paper boots to keep 4 (they) feel warm in the snow. Paper is made from 5 (difference) materials. However， we have to 6 (understand) that paper mainly comes from trees. Some report online said it took about 17 trees to make 1 ton of paper. If we keep on 7 (waste) paper， the forests may 8 (appear) in the future. So we must save paper. We can use both 9 (side) of every piece of paper， use glasses instead 10 paper cup， etc. In a word，we should keep a balance between using paper and protecting frees.
