单选题 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.

【正确答案】 A

【答案解析】[分析] 细节题型。根据第四段的the Bureau reports more than 280 MSAs， which together account for 75 percent of the US population，即75%的人住在MSA，但不单是the Eastern Corridor，California coast地区，因而排除B。第四段是对megapolis的介绍，不是对文章的总结，排除C。选项D的内容没有在文中提到。