Final answer:
When being passed by another vehicle, you should stay well over to the right, maintain your speed, and not accelerate. Being prepared to cooperate with the other driver, if necessary, is also crucial for safety.
Step-by-step explanation:
When another vehicle is passing you, there are several safety measures you should keep in mind to ensure a smooth passing process. First and foremost, you should maintain your speed and stay well over to the right. It is important not to accelerate; instead, you should leave the initiative to the driver who is passing. As the other vehicle begins to pass, you must not increase your speed, as this can lead to dangerous situations and potential accidents. Instead, by maintaining your speed, you allow the other driver to predictably and safely complete the maneuver.
Additionally, while it is not always necessary to check the right shoulder specifically (as that would be more important when you are about to turn or change lanes to the right), you should remain vigilant and be prepared to cooperate with the passing vehicle when needed. This can include slight adjustments to your position on the road if the situation requires it to facilitate safer passing.
In summary, the correct approach when being passed by another vehicle encompasses all the considerations given in the question: staying to the right and maintaining speed, not accelerating, and being prepared for any necessary collaboration. Thus, the answer to the question of what to do when another vehicle is passing you would be. All of the above.