Comprehensive and Detailed Explanation:

Under the FIDIC Red Book 2017 (similar principles apply in other editions), Sub-Clause 4.1 (“Contractor’s General Obligations”) and Sub-Clause 3.4 (“Delay Damages”) require both Employer and Contractor to notify the Engineer in advance about any events or circumstances which maydelay the worksoradversely affect the Contractor’s personnel or progress. This early notification ensures proper management and mitigation of risks that could impact the project timeline or quality.

Option A (Delay the execution of the Works or a Section)is a core reason for notification since delays affect the critical path and programme, requiring possible extensions or adjustments.

Option C (Adversely affect the work of the Contractor's Personnel)is also a valid reason because issues affecting workforce productivity or availability can impact project delivery.

On the other hand:

Option B (Decrease the Contract Price)isnota reason to notify. Changes in contract price usually arise from variations or claims but are not a “known or future event” requiring prior notification unless linked to a variation or compensation event.

Option D (Increase the performance of the Works when completed)is positive and does not negatively affect project progress or cost; therefore, it is not a reason for advance notification under these contract provisions.

Thus, the twonot applicablereasons are B and D.