Explanation:

Keyboard, monitor, and cabinet (referring to the computer case or chassis) are all physical, tangible parts of a computer system. These physical components are collectively known as computer hardware. Therefore, option (c) 'Computer hardware' is the correct classification. Option (a) 'Control unit' is a specific component within the CPU, responsible for directing operations, not a general category for these items. Option (b) 'Computer software' refers to the programs and data that run on the hardware, which are intangible. Option (d) 'Storage unit' is a specific type of hardware component (e.g., hard drive, SSD) but does not encompass all three items listed. These are fundamental physical components of a computer.