Final answer:
Intra-sector systems are systems in which various related subsystems within a single sector are interconnected and work together. The term 'intra' refers to 'within,' signifying that all interactions occur inside the sector.
Step-by-step explanation:
Intra-sector systems can be best described as systems in which the various subsystems are connected. These systems exist within a single sector, meaning they include different but related processes, departments, or components that interact with each other inside that particular area or field. The function of an intra-sector system is to ensure that the subsystems work together harmoniously to achieve the sector's overarching goals.
As for the provided reference on what an isolated system is, the correct answer is not directly related to the question about intra-sector systems. However, for clarification, an isolated system (answer b.) is a system in which the net external force is zero, meaning no energy or matter is transferred into or out of the system.