Explanation:

To effectively work on a computer, both 'hardware' and 'software' are absolutely essential. Hardware refers to the physical components like the CPU, memory, and input/output devices, which provide the physical infrastructure. Software, on the other hand, consists of the programs and instructions that tell the hardware what to do, enabling it to perform tasks. Without hardware, there's nothing to run the software on, and without software, the hardware is just inert machinery. A 'scanner' is an optional peripheral device for inputting images, not a fundamental requirement for general computer operation. Therefore, the combination of both hardware and software is necessary.