Is used as a pre-selected background which will be replaced by

1. Green screen 2. any background

Explanation:

The process of using a green screen as a pre-selected background and replate it for any background is called Chroma Keying. It's a technique for visual effects and post-production, used to put together two different images or videos, by combining visual elements from separate sources into a single image, in order to "make believe" that all of those elements are part of the same scene, a process called Layering. The technique is mostly used to remove a background from the subject of a photo or video, and replace it with another background. This is done with the help of a backdrop of brightly colored fabric or paint, also known as green/blue screen, due to the color of the backdrop. But the technique can be done with background of any color that is uniform and distinct, however, green and blue are the prefered colors as they differ the most in hue from most human skin colors, and since Chroma Keying is basically picking up a color and replacing it with a different image, other colors that are also present in the main subject might be picked up during the process and replaced with the other image. Blue and green are generally easier to chrome key. However green screens are still more commonly used for a few reasons, one of them is that some people wear blue clothing, and also because the green used in them has the highest luminance of all the color channels (RGB)