What three components are required to form a complete circuit?

A complete circuit is essential for electrical systems to function properly, and the correct components for forming such a complete circuit are a power source, an operating unit, and conductors.

The power source provides the necessary voltage, supplying electrical energy to the circuit. The operating unit, which can be an electrical device like a motor or light bulb, is where the electrical energy performs work. Conductors facilitate the flow of current, connecting the power source to the operating unit, enabling the overall operation of the circuit.

In contrast, while switches, fuses, and loads are important components in electrical systems, they do not specifically define the formation of a complete circuit. Similarly, actuators, contacts, and relays are specific components often used in control systems but do not encompass the broader concept of what makes a complete circuit in the general sense. Lastly, circuit boards, power supplies, and capacitors play significant roles in many electronic systems but do not serve as the fundamental components required to establish a circuit as described in the correct option.