Identify the correct statements about Friedmann's core-periphery model.

A. The core region is the focus of economic growth with an urban nucleaus.

B. Around the core downward transitional areas are in the process of development.

C. Resource frontier areas are found around the core region.

D. Downward-transitional areas represent areas of settlement that are stagnant or declining because of decline in the resource base or industrial structure.

Choose the correct answer from the options given below: