Which option describes one reason europeans were able to gain dominance over the americas in the late 1400s and early 1500s?

europe’s large population forced migration to the americas.

european diseases killed many people in the americas.

europeans and africans joined forces to attack american indians.

european explorers had excellent geographic knowledge.

B. Because the diseases of the Europeans killed millions of the Natives... 

D. is not correct because the Europeans didn't live in the Americas like the natives did so they didn't know that land, as well as the natives, did.
A. is completely irrelevant it's saying the need for colonization 
C. Europeans didn't start importing African Slaves until a little while later. After they found that the Natives died to quickly from disease and such.