Which of the following should be bonded together to form the grounding electrode system if present at each building or structure?

The correct answer highlights the necessity of bonding various components together to ensure the effectiveness of the grounding electrode system. When both concrete-encased grounding electrodes and metal structures are present at a building or structure, bonding them forms a more comprehensive grounding system. This is crucial because it helps create a low-resistance path for electrical fault currents, enhancing safety by reducing the risk of electric shock and protecting equipment from damage due to surges or faults.

Concrete-encased electrodes are often a part of a building's structural framework and can effectively act as grounding electrodes due to their conductive properties. Metal structures, such as rebar in concrete, can also contribute to the grounding system, allowing for better dissipation of electric currents. By bonding these systems together, you ensure that any electrical potential is equalized across the components, further increasing the reliability and safety of the grounding system.

Other choices are limited because they either focus on only one type of electrode or fail to recognize the importance of including all relevant components in the bonding process. By excluding any aspect of the structure that can effectively contribute to grounding, the system's overall safety and performance may be compromised.