Which of the following statements best describes 21st-century migration flows to the United States? a Large numbers of immigrants and migrant workers, including skilled and unskilled laborers and many with advanced degrees, are coming to the United States from South and Central America. b Large numbers of immigrants and migrant workers, mostly unskilled agricultural laborers, are arriving to the United States from Eastern Europe, Africa, and Asia. c Large numbers of immigrants and migrant workers, mostly in the medical and engineering fields, are arriving to the United States from Western Europe and the Pacific Islands. d Large numbers of immigrants and migrants workers from the United States, including skilled and unskilled laborers and many with advanced degrees, are going to Western Europe and Australia.