One possible version：

There are differences between high school in China and that in the United States. High school in China lasts three years, while in most US states four years. In China, students are in fixed classes and classrooms. Every day they study hard for about 10 hours and have a solid knowledge. But in the United States, students don’t have fixed classes or classrooms and they go to their teachers’ offices for classes. They spend about 8.5 hours on study a day. They are lively and good at activities organized by themselves. However, in China, the students’ extra curricular activities are mostly organized by schools and classes.