A fire alarm system must operate on standby for a period of not less than ____ days followed by at least ____ minutes of alarm.

The correct answer is based on the requirements specified for fire alarm systems, which are designed to ensure reliability and effectiveness in emergency situations. A fire alarm system must be capable of operating on standby for a minimum of 7 days. This duration is crucial because it allows the system to maintain its readiness without external power or interventions. Moreover, after that standby period, the system must demonstrate its functionality by operating in alarm mode for at least 4 continuous minutes. This ensures that when an actual fire situation arises, the alarm will sound long enough to alert occupants and facilitate timely evacuation or response.

The specifications are aligned with established guidelines in fire safety codes, which prioritize both reliability and performance to protect life and property effectively. The other options do not meet these necessary requirements for standby duration and alarm signaling time as outlined in the regulations for fire alarm systems.