Paul wants to make sure his ads reach users who visit a popular delivery app. Which dimension will he choose when setting up his bid multipliers?

Paul should choose "Apps and URLs" because this dimension allows him to target or exclude specific mobile applications and websites where his ads might appear. By selecting this option, he can input the URL or app ID of the popular delivery app to ensure his ads are shown to its users. "Geography" would target users based on their physical location, not their app usage. "Demographics" would target based on age, gender, or household income. "Audience Lists" are pre-defined groups of users based on their past behavior or characteristics, which might include app users but is a broader category; "Apps and URLs" provides the direct control Paul needs for a specific app.