• Add a Display & Video 360 macro to the Floodlight Tag
• Set the Floodlight tag to accept Dynamic tags
• Add a custom variable for audience targeting
• Assign the Floodlight tag to an audience list

The correct answer is: Assign the Floodlight tag to an audience list

Explanation: If you’ve linked your Floodlight configuration to your advertiser, you can target new audience lists in Display & Video 360 as soon as they’ve been created as Floodlight activities in Campaign Manager. Occasionally, it may take up to an hour for a newly created Floodlight activity to appear in Display & Video 360.

Read more here: https://support.google.com/displayvideo/answer/2949947