【英语时差8,16】变黄了的旧书

（单词翻译）

 Open an older book and you may find the paper yellowed around the edges. Even older books fall apart as you turn the pages. But you might be surprised to learn that the pages in some of the oldest books are still white and turn easily without cracking. During the last 500 years, the quantity of paper being produced has increased dramatically, but the chemical composition of modern paper causes it to turn yellow and crumble¹ faster. Paper can be made from almost any form of cellulose that can be shredded² into tiny fibers³ and mixed into a watery⁴ pulp⁵. Since cellulose is found in all plants, most plant matter can be used to make paper. In the pulp, the cellulose fibers are partly dissolved so that when the sheet of paper is dried, the molecules⁶ of different fibers bond to each other.