Program control instructions alter the program __________ of a PLC from its normal sequence.

Program control instructions are key components in a PLC (Programmable Logic Controller) that modify how the program operates during execution. They specifically alter the program's flow of control, determining how the program executes its instructions based on certain conditions or events.

When the question refers to the program's scan, it is addressing the manner in which the controller processes its logic and tasks. The scan cycle typically represents how the PLC reads inputs, processes the program, and updates outputs in a cyclic manner. By using program control instructions, such as jumps, branches, or subroutine calls, the normal scan sequence can be intentionally deviated from to accommodate specific operational requirements. For example, a jump instruction might redirect the controller to skip certain instructions or repeat others based on real-time inputs or conditions, effectively changing the order or flow of processing.

In this context, while other terms like flow, sequence, and output are related to the functioning of a PLC, the term that accurately reflects the concept of altering the regular operation of the program during its execution is the scan. Therefore, focusing on how program control instructions impact the scan cycle elucidates why this answer is fitting in the context of PLC operation and control.