Stephen is a professor at a university. He tells his students that rich countries continue to stay rich because they control the economies of poor countries. He also states that they exploit the poor countries because workers in poor countries depend on external markets for jobs. He argues that rich countries set prices for agricultural products exported by poor countries regardless of market values. Which of the following theories is Professor Stephen describing to his students? a. Feminist theory b. Functionalist theory c. Modernization theory d. World-system theory e. Symbolic interaction theory