Which of the following is true regarding electrical relays?

Electrical relays are devices that use an electromagnet to control the connection of circuits. One of the key features of relays is their ability to control multiple circuits simultaneously, which is why the statement is true. This means that a single relay can switch several circuits on or off based on the control signal it receives.

This multiple circuit control capability is particularly useful in various applications, such as in aircraft systems, where different systems need to be activated or deactivated based on specific conditions without requiring multiple manual switches.

Other options like the idea that relays only operate at high voltages, require constant manual operation, or are primarily used in lighting circuits do not accurately describe the versatile and widely applicable nature of relays. In reality, relays can operate at a variety of voltage levels, can function automatically based on electrical signals rather than needing manual intervention, and while they can be used in lighting, their applications extend far beyond that single purpose to include safety systems, automation, and various control functions in different electrical systems.