Answer: D. Whites moved to the suburbs.
White flight is a phenomenon that started in the 1950s and 1960s in the United States. The term applies to the migration of white families from the city to the suburbs, or to less urban areas. This caused segregation in various cities, as it made the suburbs more "white," while the cities remained a mixture of various minorities. The reasons for this are unclear, but they most likely include population and economic pressures.