图中 R₁、 R₂、 R₃分别表示三个不同等级的城市，据图完成问题。

小题1:与三个城市服务半径相对应的可能是

A．R₁—地级市，R₂—县城，R₃—集镇

B．R₁—扬州，R₂—南京，R₃—上海

C．R₁—省城，R₂—县城， R₃—乡镇

D．R₁—北京，R₂—上海，R₃—重庆小题2:有关三个城市的叙述正确的是  

A．R₁服务半径最小，服务范围最大

B．R₂比R₁提供的职能种类少

C．R₃的城市级别最高

D．R₃的服务范围小于R₂

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 that 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 adjacent metropolitan areas. One of the most obvious megapolises includes a chain of hundreds of cities and suburbs across 10 states on the East Coast from Massachusetts to Virginia, including Boston, New York, and Washington, D.C. In the Eastern Corridor, as it is called, a population of 45 million inhabitants is concentrated. Another megapolis that is growing rapidly is the California coast from San Francisco through Los Angeles to San Diego.

Why does the author mention the Eastern Corridor and the California coast in Paragraph 4

A. As examples of megapolises.
B. Because 75 percent of the population lives there.
C. To conclude the passage.
D. The Bureau of the Census is located there.