In the United States, children start school when they are five years old. In some states they must stay in school until they are sixteen. Most students are seventeen or eighteen years old when they leave secondary（中等的） schools. There are two kinds of schools in the United States: public schools and private（私立的）schools . Most children go to public schools. Their parents do not have to pay for their education because the schools receive money from the government. If a child goes to a private school, his parents have to get enough money for his schooling. Some parents still prefer private schools, though they are much more expensive. Today about half of the high school students go to universities after they finish the secondary school. A student at state university does not have to pay very much if his parents live in that state. But many students work while they are studying at universities. In this way they develop good working habits and live by their own hands.

小题1: Children can go to school at the age of four in the U.S.

小题2:Most parents prefer to send their children to private schools in America.

小题3:About fifty percent of high school students can go on to universities after they leave the secondary school today.

小题4:Lots of American students go to universities by depending on their parents completely (完全地).

小题5:The passage is mainly about American education.

以下不是急冷油循环泵抽空的原因是（）。

A.入口过滤器堵塞

B.急冷油粘度太高

C.汽油分馏塔塔釜无液面

D.泵机械故障

E.折流板掉下堵住入口孔