The Migration of Almost a Million Blacks from the South

The migration of almost a million blacks from the South in the 1920s revealed that

A) the agricultural sector of the American economy was in dire straits well before the Depression began,forcing southern blacks to find work elsewhere.
B) the agricultural sector of the American economy was booming,and white workers were pushing blacks out of their agricultural jobs.
C) most industries in the North,enjoying unprecedented prosperity,were willing to hire black workers on equal terms as white workers,leading to an exodus from the South.
D) the soil of the South was no longer fertile enough to support the cultivation of cotton on which the region's economy had previously depended.