Answer: D. They operate on a variety of spatial scales.
Step-by-step explanation:
The model of core-periphery relationships represents the fact that how economic, cultural and political powers are distributed spatially among the dominant regions of the core, more marginal, dependent on the peripheral and semi-peripheral regions.
These core-periphery relationships operate on the variety of the spatial scales. The core includes the powers of the world and that of countries which consists of majority of wealth in the planet. The periphery includes those countries that does not include the global wealth.