• On screen
• Sample website
• Custom URL
• Blank page

The correct answer is: Blank page

Explanation: 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 on the 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