Economic activity varies greatly from one part of the country to another， with many industries being largely dependent on a certain city or region； New York City is the center of the American financial， publishing， broadcasting， and advertising industries； Silicon Valley is the country，s primary location for high technology companies， while Los Angeles is the most important center for film production. The Midwest is known for its reliancereliance n.信任， 信心， 依靠， 依靠的人或物 on manufacturing and heavy industry， with Detroit serving as the center of the American automotive industry； the Great Plains are known as “the breadbasket of America” for their tremendoustremendous adj.极大的， 巨大的 agricultural output， while Texas is largely associated with the oil industry； the Southeastern U.S. is a major hub for medical research， as well as many of the nation，s textiles manufacturers.
Several countries continue to link their currency to the dollar (such as the People，s Republic of China) or even use it as a currency (such as Ecuador)， although this practice has subsided since the collapse of the Bretton Woods system.
The largest trading partner of the United States is Canada (20%)， followed by Mexico (12%)， China (Mainland 10%， Hong Kong 1%) and Japan (8%). More than 50% of total trade is with these four countries. In 2003， the United States was ranked as the third most visited tourist destination in the world； its 40.4 million visitors ranked behind France，s 75 million and Spain，s 52.5 million.
Education
In the United States， education is a state， not federal， responsibility， and the laws and standards vary considerably. In most states， all students must attend mandatory schooling starting with kindergarten and following through twelth grade (although students are permitted to drop out upon the age of 16 with the permissionpermission n.许可， 允许 of their parents/guardians). Parents may educate their own children at home (with varying degrees of state oversight)， send their children to a public school， which is free， or to a private school， where parents must pay tuition. Public schools are highly decentralized with funding and curriculum decisions taking place mostly at the local level through school boards.
After high school， students have a choice of attending either a public/state university or a private university. Public universities receive funding from the federal and state government but students still pay tuitiontuition n.学费， which can vary depending on the university， state， and whether the student is a resident of the state or not. Tuition at private universities tends to be much higher than at public universities.
American colleges and universities range from highly competitivecompetitive adj.竞争的 schools， such as Stanford University and Harvard University， to hundreds of local community colleges with open admission policies. For a complete list， see Colleges and Universities in the United States.
Language
The United States does not have an official language at federal level； nevertheless， English is the first and/or only language of the overwhelming majority of the population and serves as the de facto language： English is the language used for legislation， regulations， executive orders， treaties， federal court rulings， and all other official pronouncementspronouncement n.声明.