Answer:
Correct answer is European diseases had killed much of the native workforce.
Explanation:
As we all know around 90 percent of Natives died because of the diseases and other problems that were brought to them by Europeans. That is why they could only turn themselves to slave trade. Slaves were usually imported from Africa.
Other answers are false, especially options one and three, which have no connection with historical events. When it comes to option 4 it was actually pretty often that Africans would sell slaves to Europeans.
