According to Wallerstein's world systems theory, which countries have the highest levels of economic development?

a. core countries

b. semi-periphery countries

c. periphery countries

d. all countries inside the Brandt line

The correct answer is letter A.

Core Countries have the highest levels of economic development based on Wallerstein's World Systems Theory. This is because they tend to focus more on higher skill and capital-intensive productions compared to the rest of the world which focuses on low-skill and labor-intensive production.