Once a rural country, the United States is today a highly urbanized country, and three-quarters of its citizens now live in towns, large cities or their suburbs. This statistic makes city governments critically important in the over-all pattern of American government. To a greater extent than on the federal or state level, the city ministers(Jiffy) directly to the needs of the people, providing everything from police and fire protection to sanitary codes(卫生条例), health regulations, education, public transportation and housing. Their huge size makes the business of running America's large cities enormously complex. Only seven states of the union, for example, have populations larger than that of New York City. It is often said that, next to the Presidency, the most difficult administrative position in the country is that of Mayor of New York. The federal, state and city governments by no means cover the whole spectrum(范围) of American governmental units. The U.S. Bureau of the Census has confirmed that there are no less than 78, 218 local governmental units in the United States: counties, municipalities, townships, school districts and special districts. The county is a subdivision of the state usually—but not always containing two or more townships and several villages. New York City is so large that it is divided into five separate districts, each a county in its own right: The Bronx, Manhattan, Brooklyn, Queens and Richmond. On the other hand, Arlington County, Virginia, just across the Potomac River from Washington D.C., is both an urbanized and suburban area, governed by a unitary county administration. In most counties, one town or city is designated as the county seat where the government offices are located and where the board of commissioners(委员) or supervisors meets. In small counties, boards are chosen by the county as a whole in the larger ones, supervisors represent separate districts or townships. The board levies taxes, borrows and grants money, fixes the salaries of county employees, supervises election, builds and maintains highways and bridges, and administers national, state and county welfare programs. We can infer from the first paragraph that______.