To ensure that the background imagery appears to be in the distance, the artist would most effectively use B. create a value change from the background to foreground.
This technique relies on the principles of atmospheric perspective, where objects that are further away tend to be lighter and less saturated in color compared to those that are closer to the viewer. By using lighter values and softer details for the background, Oudry would create a sense of depth, making the background appear more distant in the composition.