The US population in the 1970s is ______ largest of the world.

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

A．California was once the most thinly populated area in the whole US
B．the top 10 states in growth rate of population were all located in the West
C．cities with better climates benefited unanimously from migration
D．Arizona ranked second of all states in its growth rate of population