Which components are essential in a fire alarm system?

The correct choice identifies the key components of a fire alarm system, which are critical for its proper functioning. The control unit serves as the central hub that monitors inputs from initiating units and manages the system's overall operation. Initiating units, such as smoke detectors and manual pull stations, are responsible for detecting the presence of fire or smoke and sending signals to the control unit. The indicating unit provides visual or audible alerts to occupants, ensuring they are aware of a fire emergency and can evacuate the premises safely.

Each of these components plays a vital role in the system's effectiveness for detecting fires and notifying occupants, thereby enhancing overall safety and response from emergency services. In contrast, the other options include items that, while related to fire safety, do not strictly define the essential components of a fire alarm system.