• Add a polite loader
• Establish a connection to your dynamic feed
• Determine the size of the screen
• Check that the Enabler has been initialized

The correct answer is: Check that the Enabler has been initialized

Explanation: An HTML5 expand to fullscreen creative is an expanding ad with two sizes, an initial collapsed size, and a dynamic fullscreen size. The Enabler is the core code library of Studio and is required for all rich media creatives. Nothing in the ad should auto-execute until the Enabler has initialized. This ensures that everything is properly loaded and Enabler methods can be accessed before a user interacts with the ad.

Read more here:https://support.google.com/richmedia/answer/4526014