阅读理解。阅读下列短文, 从给的四个选项 (A、B、C和D) 中, 选出最佳选项。
Education in the United States is compulsory for children up to about the age of sixteen. Most young people stay in school longer than that. Most graduate from high school at the age of 17 or 18.
Almost half of these high school graduates continue their education at a college or university. Education for most young people in this country is free up to the time they graduate from high school. There are private schools, but most parents send their children to public schools, where students do not pay tuition. When young people go to college, however, they must pay tuition at a public university or a private university. University costs are going up a lot：private universities have become very expensive because the government does not help them.
Who pays? The parents of children in college may have to pay more, or often students may have to find jobs. These students have to worry about assignments and grades and also about their jobs. If they work too much at their jobs they may be absent from class or miss assignments or make too many errors on tests. They may even fail their courses and have to leave the university.
