Final answer:
An intra-sector system is a system composed of multiple components within the same sector, where independent entities are interdependent due to their shared environment. The correct option is D.
Step-by-step explanation:
An intra-sector system refers to D. a system composed of multiple components within the same sector. In the context of comparative international systems, such a system would be made up of various units—such as states in the international arena—that operate within the same domain or sector.
These states act independently, yet their behaviors are interdependent and influenced by each other due to their shared environment. This leads to a systemic effect, which arises not from the actions of individual units alone but from the terms of their interaction within the sector. The correct option is D.