A computer's hardware components, such as the processor, memory, and storage, cannot organise themselves, something must tell the computer how and when to use each of these parts. That role belongs to the operating system.
The operating system manages how the processor is shared between running tasks, how memory is allocated to programs, and how storage devices and other peripherals are accessed, essentially acting as a manager that decides how every hardware component is used at any given moment. Application programs and utilities rely on the operating system to carry out these low-level hardware decisions on their behalf.
A network refers to connected computers rather than the software managing one machine's components, and while a utility program performs specific maintenance tasks and an application performs specific user tasks, neither one is responsible for the overall management of how all the hardware components are used, that broader coordinating role belongs to the operating system.
Exam tip: whenever a question describes something that tells the computer "how to use its components" or "manages its resources," the answer is the operating system.