• Campaign Manager
• Code within the creative
• External API
• Spreadsheet

The correct answer is: Spreadsheet

Explanation: To make a creative dynamic, you connect a list of different content options (typically stored in a spreadsheet), with containers in your creative that hold text, images, or video. These containers are mostly divs or other HTML elements. You can also pass other information from the spreadsheet into a variable in your creative that’s used to control how the creative looks

Read more here:https://support.google.com/richmedia/answer/3526354