When slowing down unexpectedly, what should you do to alert others?

Answer: B — Flash your brake lights

When slowing down unexpectedly, it is important to alert others on the road to prevent accidents. Flashing your brake lights is the correct answer because it is a common and effective way to communicate to drivers behind you that you are slowing down. This action gives them a visual cue to also reduce their speed and maintain a safe following distance. Turning off the headlights, sounding the horn continuously, or waving your hand out to signal are not appropriate actions to indicate a sudden slow down and can even cause confusion or distraction to other drivers.