Answer:
D. specialization
Step-by-step explanation:
The economic concept that is best illustrated by the activities of the Italian city-states is D) specialization. The city-states were able to become wealthy and powerful by focusing on producing a specific product or providing a particular service in which they had a comparative advantage. This allowed them to become highly efficient and productive in their specialized area, and to trade with other city-states for goods and services in which they were not as proficient. This specialization and trade allowed them to become interdependent and to benefit from the advantages of a larger market, ultimately leading to their success.