The Internet has become part of teenagers' life. A news report on 3,375 students aged from 10 to 18 in seven Chinese cities found that 38 per cent of them believe they use the Internet often. While most of them get useful information and use the Internet to help in their studies, some are not using it in a good way. Many are playing online games too much. A few even visit Web sites they should not look at. A middle school teacher from Beijing warns that bad things can happen if young people spend too much time on the Internet. She had a student who used to be good at school. But then he started visiting sex Web sites. He went mad, cheated a girl and was taken away by the police. In order to help young people use the Internet in a good way, a textbook on good Internet behavior has started to be used in some Shanghai middle schools this term. The book uses real examples to teach students all about good ways of using the Internet. The book gives useful advice such as it's good to read news or find helpful information to study. Some students also make online friends. But if you are meeting a friend offline, make sure your parents know. Teachers and parents all think the book is a very good idea. This teacher said the book will be a guide for teens using the Internet. She believes it will keep students away from bad sites. "Many students are using the Internet without guidance from their parents," she said. "The book will teach students how to be a good person in the online world." The textbook mainly tells us   _  .
why we should use the Internet not to visit sex Web sites how to use the Internet correctly how to get help from others