First, Sina is the earliest of the four great inventions. Invented and put into use in the Spring and Autumn Period, it gradually spread all over the world. It plays an important role in modern human geography, navigation and military affairs, and is the prototype of compass.

Secondly, before the invention of papermaking, people used bamboo slips to write, which not only consumed raw materials, but also occupied space. After Cai Lun improved the "Cai Hou Paper" in the Eastern Han Dynasty, this problem was solved, which made it easier for people to write at low cost and preserved more works, which we used all the time in our daily life.

Third, gunpowder is the result of ancient people's eagerness to become immortal and active alchemy. It was used in the military in the Tang Dynasty and became an indispensable part of modern weapons, aerospace and architectural design.

Fourth, letterpress printing: invented by Bi Sheng in the Northern Song Dynasty, which greatly saves raw materials and can be reused. This is the prototype of a modern printer.