Final answer:
A nation-state has specific geographic territories and borders where people share a common language and culture, combining political and cultural entities into one sovereign state (A).
Step-by-step explanation:
The entity described in the question that has specific geographic territories and borders, and within which communication and transportation allow for the sharing of a common language and culture, is a nation-state. A nation-state combines the political entity of a state, which has bureaucracy, laws, and defined boundaries, with the cultural entity of a nation, which refers to a group of people connected by shared history, culture, and beliefs. Therefore, the answer to the student's question is 'A. nation-state'.
Nation-states are characterized by a centralized rule that maintains sovereignty over a territory. They build infrastructure, regulate the economy, and uphold laws. Nation-states may also form from ethnic identity, language, and a shared sense of origin. Modern-day nation-states, like France and Japan, govern themselves and strive to protect their national identity.