What must a driver do when approaching an intersection where a traffic signal light is out?

Answer: B — Come to a complete stop

When approaching an intersection with a traffic signal light that is out, it is important for a driver to come to a complete stop. The other options are incorrect because driving through the intersection without stopping can result in a collision with other vehicles or pedestrians who may have the right-of-way. Taking the lane with the most traffic may not be necessary and assuming the right-of-way can also be dangerous as other drivers may not be aware of the non-functioning traffic light.