爱迪生说：“科学需要幻想，发明贵在创新。”我们青少年要有所发明创造，就应善于观察，见微知著；敢于质疑，敢为人先；大胆想象，有求异思维。请阅读下面短文，根据短文内容完成思维导图，掌握其脉络结构及写作思路。
About two thousand years ago, there was no paper in the world. People used to carve characters in wood, stone or bamboo slips. The rich people wrote on silk or sheepskin.
A Chinese inventor named Cai Lun tried his best to improve paper. He taught people to make paper from waste materials like bark, used cloth and fishing nets. In the year around 105, paper of good quality was finally invented. It could be used for writing.
After the invention, books became more and more popular all around the world. The invention of paper is very important in the development of human civilization. Cai Lun is a great inventor we should remember all the time.
文章结构分析：
第一段（发明前）：开篇导入，介绍没有纸的情况。
第二段（怎样发明）：纸的发明历史。
第三段（发明后）：纸的作用。
请根据短文内容完成思维导图。

Material: make paper from waste materials like bark, used cloth and 4.

1. wood, stone or bamboo slips
2. silk or sheepskin
3. Cai Lun
4. fishing nets
5. in the year around 105
6. more and more popular
7. human civilization