How Did the Early Europeans Usually Obtain Their Supply of African

How did the early Europeans usually obtain their supply of African slaves?

A) They raided along the west coast of Africa, forcibly capturing large families.
B) Arabs brought slaves up to the coastal cities in Europe and Europeans bought them.
C) Europeans captured large land areas through warfare, and subjugated entire groups of people into slavery.
D) They obtained their slaves through trade with native African tribes, primarily in West Africa.