If a vehicle suddenly stops in front of a motorcyclist, what should the motorcyclist do?

Answer: D — Adjust speed, and change lanes if necessary.

When faced with a situation where a vehicle suddenly stops in front of a motorcyclist, it is crucial for the rider to maintain control and respond appropriately. Adjusting speed and changing lanes when necessary can provide a safer outcome. By reducing speed, the motorcyclist allows for more reaction time and can better assess the situation ahead. Changing lanes, if it's safe to do so, can help the rider avoid a collision entirely by moving into a position where there is more space and less likelihood of impact. While applying brakes and stopping quickly might seem like an immediate response, it could lead to loss of control on a motorcycle, especially if done suddenly. Similarly, using the horn to alert the driver may not be effective enough during a swift emergency situation, where timing and precision of movement become essential. Focused on evasive action by adjusting speed and lane positioning is often the most prudent approach in the event of sudden stops, providing greater safety for the motorcyclist.