According to the PMBOK® Guide, change requests are an output of various monitoring and controlling processes. They are formal proposals to modify any document, deliverable, or baseline.

Preventative Action: This is an intentional activity that ensures the expected future performance of the project work is aligned with the project management plan. While corrective action deals with existing deviations, preventative action is proactive. It is based on trend analysis and risk assessment to stop a potential problem before it occurs.

Examples:

Cross-training a team member because a key subject matter expert might be leaving soon.

Ordering equipment early to avoid a forecasted supply chain delay.

Adding extra testing cycles to a high-risk software module to prevent bugs in the final build.

Key Distinction: The focus is on the future. If the project manager notices that the project is currently on track but could slip due to an emerging risk, they initiate a preventative action.

Analysis of Other Options:

A. Corrective action: This is an intentional activity that realigns the performance of the project work with the project management plan. The key difference is that corrective action addresses past or current deviations (the problem has already happened).

B. Defect repair: This is an intentional activity to modify a nonconforming product or product component. It specifically targets the quality of a deliverable that has already been produced and found to be faulty.

D. Probable action: This is not a formal term recognized in the PMBOK® Guide or PMI standards.