Final answer:
When a school bus has its stop sign extended out and flashing, you must always stop to ensure the safety of the children boarding or exiting the bus.
Step-by-step explanation:
When a school bus has its stop sign extended out and it's flashing, you must always stop, regardless of the circumstances. This is because the stop sign is an indicator that children are getting on or off the bus, and their safety is of utmost importance. It is crucial to follow this rule to prevent accidents and protect the lives of students who rely on the bus for transportation.