What should be visible on a school bus when it is stopped for picking up or dropping off passengers?

Answer: A — "school bus" sign

When a school bus is stopped to pick up or drop off passengers, it is crucial that a clearly visible "school bus" sign is present. This sign serves an essential safety function as it alerts other drivers that they are approaching a vehicle that is actively engaged in the transport of children. The primary purpose of the sign is to ensure that motorists recognize the bus as a designated school vehicle, which, in turn, prompts them to exercise caution and reduce their speed when passing. In addition to the "school bus" sign, the proper operation of flashing yellow lights is also critical when the bus is preparing to stop, as these lights signal that the bus will soon change to flashing red lights. However, the vital element that must remain visible once the bus is stationary is the "school bus" sign. The other options, while associated with school bus safety, either serve a different purpose or are not mandatory in the same way the sign is when the bus is stopped for loading or unloading.