What must the fire guard sound when a fire is found?

The correct answer is the fire alarm pull station because it is the designated method for sounding an alarm in the event of a fire discovery. When a fire guard identifies a fire, activating the fire alarm pull station alerts the building occupants to evacuate immediately. This method ensures that the alarm is communicated promptly to everyone in the vicinity, enacting the established fire safety protocols.

While options such as the fire bell and the alarm system might play important roles in the overall emergency response, they are generally activated through the proper procedures that typically involve pulling a fire alarm station. An evacuation signal is often part of later stages in response to an alarm, but the initial action when a fire is discovered should always be to pull the fire alarm, as this is the primary means of notifying occupants of an immediate threat.