填空题

Americans are a highly (36) people. What factors cause them to move The desire for economic betterment is (37) the most important force inducing migration.
Thus the (38) and direction of migration are usually determined by (39) difference in (40) factors, as (41) by such ones as differences in employment (42) and differences in the (43) and the price of land for farmers. Here is a case showing clearly the trend of migration in the country. When New England was declining in textile industry, there were many people moving out of it. When California has the phenomenal growth of electronic industry, there is a large scale of in- migration to the state. However, (44) .
Since 1970, there has appeared a new trend of migration in America. More Americans migrated from cities to suburbs. There are several factors for this phenomenon. The construction of express highways made it possible for people to live farther away from their jobs. (45) . Besides these economic and technological changes, important social factors were involved. Suburban areas offered more living space than cities and less pollution. Many middle-income families now live in the suburbs. (46) . Despite the new trend in migration, about 70 percent of American population are still living in metropolitan areas.