In What Manner Did the Portuguese Seize Most of the Slaves

In what manner did the Portuguese seize most of the slaves that were transported from Africa?

A) They captured them in raids into the African interior.
B) They traded for them with African rulers.
C) As a result of the defeat of most of the African kingdoms, the Portuguese obtained a ready supply of slaves.
D) They purchased them from the Muslim slave traders of the east African trading cities.