Self-service library, the subway station, only needs his ID card and pays 100 yuan. After that, he just needs to swipe his ID card. The 25 self-service library books set up by the city library on the street are bound to wuhan tong (versions) with ID cards when borrowing books for the first time, and no cash is paid. Finally, lock 100 yuan in wuhan tong and unlock it when returning the book. The money is in your own wuhan tong and can be used elsewhere. Subway library 100 yuan deposit can also be refunded. The difference is that you will use a different card to borrow and return books in the future. One is your ID card, and the other is wuhan tong. It is said that the subway library will borrow books from wuhan tong in the future.