Which of the following circumstances encouraged the growth of the system
described in the passage?

A. Population pressures in Africa led some to exchange their labor for
resettlement.

B. Colonies needed cheap sources of labor to supply the ambitions of
European nations.

C. African leaders lacked sufficient natural resources to trade for
European finished goods.

D. Conflict in the Americas provoked European powers to use Africans
to bolster their numbers.