What must you do when advertising a vehicle as a demonstrator?

Answer: C — Specify it is a demonstrator

When advertising a vehicle as a demonstrator, it is important to specify that it is indeed a demonstrator vehicle. This means that the vehicle has been used as a display or test vehicle by the dealership but is still technically a new vehicle. This information is important for potential buyers to know, as it may impact the perceived value and price of the vehicle. While the other options may also be relevant when advertising a vehicle as a demonstrator, it is crucial to explicitly state that it is a demonstrator to avoid misleading or confusing potential buyers. Therefore, option C is the most correct answer.