So yesterday, I borrowed this book from the Shanghai Library. And it was really easy and convenient to borrow from there as well. >> Of course, Shanghai Library is one of the biggest libraries in China. There are a great variety of books in Shanghai Library. Do you know that the earliest books produced were made of bamboo's leaves and silk? >> Really? I can only imagine how expensive and heavy each book was. >> Well that's why a Chinese official, Cai Lun, from Han dynasty, invented paper and then improved the paper making process. His idea of paper making came from using the bark of trees, rags of clothes, and fishing nets. Then people can use paper to make books, books became cheaper and lighter. >> Okay, well, paper was a great revolution in the history of human communication. And it helps spread the usage of both books and knowledge as well. >> That's true. With the development of technology, books became electronical. I heard that in the US, there are more books published online than distributed in hard copy. >> Well yeah, because e-books generally are very easy to come across and to get a hold of. And you can always read them anywhere on your computer, or your tablet, or your smart phone. >> There's also a concern that with the wider spread of e-books, physical books will soon disappear in the future. >> Maybe, but personally, I prefer to read from a book. I find it more comfortable reading on paper.