Final answer:
When driving on a one-way street and an emergency vehicle approaches with flashing lights, you must drive toward the nearest roadside and stop.
Step-by-step explanation:
When driving on a one-way street and an emergency vehicle using its flashing lights approaches your vehicle, you must drive toward the nearest roadside and stop (option b).
This is the standard procedure to allow the emergency vehicle to pass freely and safely.
By moving to the nearest roadside and stopping, you are creating a clear path for the emergency vehicle to pass and ensuring that no obstacles or other vehicles obstruct its way.