In Reference to Black Family History, the "Great Migration" Refers

In reference to Black family history, the "Great Migration" refers to

A) The transport of slaves from Africa to the Americas.
B) Twentieth century movement out of the rural South.
C) Movement on the underground railroad during slavery.
D) Movement to rural areas immediately after the Civil War.
E) Movement from cities to suburbs in the 1980s and 1990s.