In terms of passing a streetcar, what is a key requirement for drivers?

Answer: B — To stop when necessary

When it comes to passing a streetcar, a crucial requirement for drivers is to stop when necessary. This is primarily for the safety of passengers who may be boarding or alighting from the streetcar. Streetcars often have designated stops where people will get on or off, and if the streetcar is stationary, it indicates that pedestrians could be nearby. Stopping allows drivers to ensure that the area is clear of any pedestrians and provides a safe environment for those who may be crossing or approaching the streetcar. In urban settings, where streetcars are common, failing to stop when required could lead to accidents, especially if a passenger unexpectedly steps onto the road. While slowing down may be appropriate in certain situations, it doesn't guarantee the safety of pedestrians as effectively as stopping would. Keeping moving if there's space might seem practical, but it can endanger passengers who might be in proximity to the streetcar's doors. Flashing headlights is generally used as a warning signal rather than a compliance measure. Thus, stopping when necessary is the best practice to ensure everyone's safety around streetcars.