The invention I will introduce to you is a little hard to describe. It's one of the four greatest inventions in ancient China. It is called the Movable-Type Printing. You can think it as a printer that existed 12th centuries ago. You can imagine yourself living during the period about 700 years ago, if you wanted to read books, what would be in your hands? A phone? A computer? Or a paper book? In fact, a paper book was more likely to appear on your table. As more and more people around you like reading, the hand-copied books couldn't meet the demand. Then block printing was invented and the speed of printing was increased. But when a book was to be printed, we needed a lot of wooden blocks which were engraved with Chinese characters. After printing a book, these wooden blocks were useless. So, a man called Bi Sheng who might be one of your friends engraved the characters on small pieces of cubic clay and heated them until they became hard enough. Then, he placed these movable characters to print different articles. After everything was prepared, people needed to put ink on them, then put a piece of paper on the character and pressed around, finally a page of a book was printed. All the movable characters would be removed and were used to print the next page. It saved a lot of money and time. More and more people could read a variety of books.