Answer: Object
Explanation: Object is a major part of a system that has the relevance with the real world entities.The objects are used in the object-oriented approach in the operating system for the development and maintenance of it.
It is the component that comprises of the two major factors-code and data. The code and data are for the determination of the behavior and the status of the object respectively. Other options are incorrect because they don't operate as the building block for a system.