Why did the Europeans need slave labor in the colonies?

Which of the following is an example of how the transition toward a more global economy affected the sale of goods? a. africa's transition to becoming the largest producer of manufactured goods and establishing a monopoly over trans-atlantic trade b. an increase in the number of countries that adopted isolationist policies to preserve native cultures c. south america's transition away from the production of manufactured goods to a dependency on agricultural products d. the turn away from small trade goods, such as silk and spices, and toward bulk items such as slaves and manufactured goods