You'd like to add mobile ads to your current campaign, but some creatives are already mobile-optimized and could be appearing on mobile websites. What's the first consideration you should look at within the Campaign Manager 360 account to make sure of delivery and to reach your goal?

The correct answer is to examine your trafficking settings. Before adding new mobile ads, you need to ensure that your existing trafficking settings in Campaign Manager 360 are configured to deliver mobile-friendly sizes and formats. This step confirms that your current setup can accommodate and properly display ads on mobile devices, preventing issues with creative delivery and ensuring existing mobile-optimized creatives are served correctly. Reviewing the Cross-environment Report is useful for analysis but not the first step for ensuring delivery of new mobile ads. Configuring the account to include apps, mobile devices, and tablets is part of trafficking settings, but "examining trafficking settings" is a more comprehensive first step. Using mobile-friendly sizes and formats is a best practice for creative development, but the question asks about existing creatives and delivery, making trafficking settings the primary concern.