What Best Describes the Reason for the Large Migration of African-Americans

What best describes the reason for the large migration of African-Americans from the south to the north during the 1920s?

A) This movement was just a continuation of the same trend that had been occurring in large scale since the end of the Civil War.
B) African-Americans moved north to reunite families that had been divided during the many years of slavery.
C) The African-Americans who had worked in the south had mostly been employed in the manufacturing sector, which suffered a downturn in the 1920s.
D) Employers in the North who had traditionally hired many immigrants had to search elsewhere when immigration restrictions were imposed.