Final answer:
Flashing yellow lights on a school bus indicate that the bus is about to stop. It is a safety precaution to alert motorists to slow down and be prepared to stop as students may be crossing the road.
Step-by-step explanation:
Yellow lights flashing on a school bus typically indicate that the bus is about to stop to either pick up or drop off students. It's a warning signal for motorists to slow down and prepare to stop as the bus may soon activate the red lights indicating that the bus is stopped and children may be crossing the road. This safety feature helps protect students getting on and off the bus by alerting nearby drivers to the upcoming bus stop.
While other options like the bus about to turn, experiencing a mechanical issue, or being out of service could have lights or signals as indicators, they usually have their own distinct sets of lights or signage. In the case of a school bus, the flashing yellow lights serve a specific purpose in the safety procedures while the bus is in service transporting students.