Final answer:
If vehicle B is driving too closely behind you, you should maintain a steady speed to avoid the risk of an accident. Do not speed up or sound your horn; instead, change lanes safely when possible.
Step-by-step explanation:
If you are in vehicle A and vehicle B is driving too closely behind you, the safe and recommended action is to C. Maintain a steady speed. By keeping a consistent speed, you avoid the risk of an accident caused by sudden speed changes. It's important not to speed up since that could result in you driving unsafely for the conditions or exceeding the speed limit. It's also not advisable to sound your horn in this situation, as it doesn't address the problem and could potentially escalate the situation. If the problem persists, consider changing lanes safely when possible to let the vehicle pass.