[单项选择] The fact that most Americans live in urban areas does not mean that they reside in the center of large cities. In fact, more Americans live in the suburbs of large metropolitan areas than in the cities themselves. The Bureau of the Census regards any area with more than 2,500 people as an urban area, and does not consider boundaries of cities and suburbs. According to the Bureau, the political boundaries are less significant than the social and economic relationships and the transportation and communication systems mat integrate a locale. The term used by the Bureau for an integrated metropolis is an MSA, which stands for Metropolitan Statistical Area. In general, an MSA is any area that contains a city and its surrounding suburbs and has a total population of 50,000 or more. At the present time, the Bureau reports more than 280 MSAs, which together account for 75 percent of the US population. In addition, the Bureau recognizes 18 megapolises, that is, continuous adj
A. One of the 10 largest cities in the United States.
B. One of the 18 largest cities in the United States.
C. One of the l00 cities between Boston and Washington.
D. Any number of continuous adjacent cities and suburbs.