A couple of years ago, individuals can only take courses at real schools. In other words, only when they go out to schools by themselves will they have lessons which they want to have. However in recent years, with the development of internet and education mode, online teaching has become increasingly common. This kind of teaching mode means that a student just needs to have classes sitting in front of a computer at home, which appealing to lots of people. It is widely acknowledged that online teaching has its apparent merits. First and foremost, shared resources online are accessible to all people, which costs a little at the same time. This featur...