[单项选择]　　Emerging from the 1980 census is the picture of a nation developing more and more regional competition, as population growth in the Northeast and Midwest reaches a near standstill. 　　This development―and its strong implications for US politics and economy in years ahead―has enthroned the South as America’s most densely populate region for the first time in the history of the nation’s head counting. 　　Altogether, the US population rose in the 1970s by 23.2 million people―numerically the third-largest growth ever recorded in a single decade. Even so, that gain adds up to only 11.4 percent, lowest in American annual records except for the Depression years. 　　Americans have been migrating south and west in larger numbers since World War Ⅱ , and the pattern still prevails. 　　Three sun-belt states―Florida, Texas and California―together had nearly 10 million more people in 1980 than a decade earlier. Among large cities, San Diego moved from 14th to 8th and San Antonio from 15th to 10th―
A. people in favor of the trend of democracy
B. advocates of migration between states
C. scientists engaged in the study of population
D. conservatives clinging to old patterns of life