Final answer:
Inspections of excavations must be held at the beginning of the shift and as needed, ensuring the worksite remains safe due to the conditions that can alter rapidly affecting workers' safety.
Step-by-step explanation:
The correct option is Option 3: at the beginning of the shift. A competent person must inspect all excavations, adjacent areas, and protective systems daily, at the beginning of the shift, and as needed throughout the shift to ensure the safety of the workers. This is because conditions in and around the excavation site can change rapidly - due to factors such as weather, vibrations, and previous work activities - potentially leading to hazards. Therefore, inspections are necessary at the beginning of each workday and as often as necessary during the course of the work to maintain safety.