Before starting an aircraft's engine, what must be done regarding anti-collision lights?

The correct choice emphasizes the importance of safety protocols regarding anti-collision lights prior to engine start. Anti-collision lights are crucial for ensuring visibility to other pilots and ground personnel, helping to prevent accidents in busy areas such as taxiways and ramp surfaces.

Turning on the anti-collision lights immediately before starting the engine indicates that the aircraft is about to be in operation, alerting anyone nearby that the aircraft is "live" and may start moving. This precaution helps maintain a safe operational environment and aligns with standard safety practices in aviation.

The other options lack an understanding of the operational safety protocols, as they either suggest that the lights can be activated at inappropriate times or not at all, which could compromise safety on the ground.