Migratory Labor Developed in Africa During the Last of the Colonial

Migratory labor developed in Africa during the last of the colonial era because

A) the Europeans took the only jobs within their own colonies.
B) work was almost impossible to find except in cities, in mines, and on plantations.
C) Europe had introduced a cash economy, and Africans had to go where the paying jobs were.
D) both a and b
E) both b and c