Final answer:
The basic structure of a computer system is correctly represented by option 4, which includes the CPU, memory, I/O subsystem, and bus. These components are the core of computer functionality at physical, design, and user interaction levels.
Step-by-step explanation:
The basic structure of a computer system is represented by the components that handle processing, storage, and interaction with other devices and the user. Out of the provided options, number 4, which lists the CPU, memory, I/O (Input/Output) subsystem, and bus, correctly represents the fundamental components of a computer system. This setup reflects different levels of computer architecture, ranging from the physical level, where electronic changes happen, to the design level, which involves programming, and the commonsense level, as seen by the user interacting with applications for various purposes such as word processing or solving equations. Early computers, like the HB85B from the 1980s, paved the way for today's advanced computing systems, which are integral in fields like engineering and science for complex calculations, and in everyday life for tasks like communication and entertainment.