For excavations 5 feet or deeper, a protective system must be implemented unless in stable rock to ensure safety and prevent cave-ins. Protective systems include trench boxes, shoring, and sloping. Therefore, the correct answer is A. A protective system.
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For excavations 5 feet or deeper, a protective system must be implemented unless the excavation is in stable rock to prevent cave-ins. Other options like guardrail systems or attendants do not specifically address the safety of excavation sites. Proper protective systems are essential for the safety of workers in deep digs. ;