Explanation:

Pipelining is a technique in computer architecture that improves instruction throughput by allowing multiple instructions to be processed in different stages of execution concurrently. To achieve this concurrency and keep the pipeline busy, a continuous flow of instructions is essential. Option A, 'Instruction execution', is a stage within the pipeline, where the actual operation specified by the instruction is performed. While it's part of the pipeline, it's not the *requirement* that enables the pipelining strategy itself. Option B, 'Instruction pre-fetch' (or instruction fetch), is a critical requirement for pipelining. It involves retrieving instructions from memory ahead of time, before they are needed by subsequent stages of the pipeline (like decode or execute). This ensures that the pipeline stages are always supplied with instructions, minimizing idle time and maximizing throughput. Option C, 'Instruction decoding', is another stage in the pipeline, where the fetched instruction is interpreted to determine the operation to be performed and the operands involved. It's a component of the pipeline, not the overarching requirement for the strategy. Option D, 'Instruction manipulation', is a broad term and not a specific, recognized stage or requirement in the context of CPU pipelining. Instructions are processed and transformed, but 'manipulation' isn't the precise term for a core requirement. Therefore, the ability to pre-fetch instructions is fundamental to the effective operation of a pipeline strategy, as it ensures a steady supply of work for the pipeline stages.