Explanation:

The question asks for the general term that defines all the physical components of a computer system. Option (b) 'hardware' is the correct and comprehensive term for all tangible, physical parts of a computer, including the CPU, memory, storage devices, input/output devices, and the motherboard. Option (a) 'software' refers to the intangible programs, data, and instructions that run on the hardware. Options (c) 'ALU' (Arithmetic Logic Unit) and (d) 'control unit' are specific sub-components within the Central Processing Unit (CPU), which itself is a piece of hardware. While the ALU and control unit are physical, 'hardware' is the broader term that encompasses all physical components, not just these specific parts of the CPU.