Why did the use of african slaves increase in the americas during the 1500s?

a.
native americans did not know how to harvest sugar cane.

b.
portuguese colonists needed slaves to labor in their clothing factories.

c.
it was more efficient to import slaves from africa than from other places.

d.
native american populations had declined.

Try to answer all questions if possible i will take anything this is worth 30 ! ! 1. what rights do citizen's have in a monarchy? 2. what countries practice monarchy? 3. what is one advantage of a monarchy? 4. what is one disadvantage of a monarchy? 5. what rights do citizen's have in a dictatorship? 6. what countries practice dictatorship? 7. what is one advantage of dictatorship? 8. what is one disadvantage of dictatorship?