What must a driver do when approaching a flashing yellow light?

Answer: B — low down and proceed with caution

When approaching a flashing yellow light, a driver must proceed with caution. This means that they should reduce their speed, look out for any potential hazards, and be prepared to stop if necessary. Option A, topping, is incorrect because a driver should not come to a complete stop at a flashing yellow light unless it is necessary for safety reasons. Option C, turning right, is incorrect because a flashing yellow light does not indicate a specific direction to turn. Option D, speeding up, is incorrect because a flashing yellow light is a cautionary signal, and increasing speed can be dangerous.