What is unlawful when encountering a school bus with flashing red lights and a stop arm extended?

Answer: C — All of the above

The correct answer focuses on the importance of adhering to the law when it comes to the safety of children near school buses. When a school bus has its flashing red lights activated and an extended stop arm, it indicates that children may be getting on or off the bus. Therefore, it is unlawful to pass a school bus in this scenario, as doing so poses significant risks to children's safety. The law also encompasses the need to exercise caution near school zones, intersections, and railroad crossings; however, the critical aspect remains that passing a school bus under these conditions is both dangerous and illegal. This emphasizes the priority placed on protecting children during school pick-up and drop-off times, making the action of passing a bus when it is stopped with its safety signals active the most severe violation in this context.