I would go with D because they were cruel to slaves, if they got sick during the trip to Americas they were thrown over board and sometimes they were covered by a type of insurance so it didn't matter if they lost some slaves on the way.
If its multiple answer i would go with B and D. Europe would send guns and other things to the people who give slaves to the Americas then the Americas would send Europe raw materials that Europe didn't have like sorts of food or animals.