To preview a creative on a blank page, what option should be selected from the dropdown?
When you first preview a creative, it will display automatically on a blank screen in Desktop mode. Use the drop-down menus at the top to change how the preview is displayed. To view the creative on a blank page, select Blank. Open the creative in a new window on a blank page, by clicking Blank preview in blank screen. This will allow you to test any creative events or behavior specific to one creative size.
Read more here: https://support.google.com/richmedia/answer/2453372