What must a driver do when passing a streetcar that has stopped to take on and let off passengers?

Answer: B — Stop and proceed only after the streetcar doors are closed

When passing a streetcar that has stopped to take on and let off passengers, the driver must stop and proceed only after the streetcar doors are closed. This rule is in place to ensure the safety of passengers who are getting on or off the streetcar. Passengers may not be fully aware of their surroundings, and they could step into the roadway without looking for oncoming traffic. Stopping allows a safe environment for these passengers and minimizes risks of accidents. This action is a critical part of traffic safety regulations when interacting with public transport vehicles. It's essential for drivers to exercise caution and patience in these situations, prioritizing the safety of vulnerable road users. Ensuring that the streetcar doors are closed before proceeding provides a clear indication that it is safe to continue driving.