All of the responses provided can be true depending on the specific plot device used and the context of the story. However, the most direct and common effect of a plot device is often to create a sense of surprise.
So, if you were to choose one response that reflects a prevalent effect of a plot device, it would be:
A plot device creates a sense of surprise.
This is because many plot devices, such as twists, reveals, or unexpected events, are specifically designed to catch the audience off guard and enhance the overall impact of the narrative.