Maria 正在为她新的领英广告推广活动进行 A/B 测试。她想确定哪种广告形式在目标客户中表现更优异。其中一个版本使用的是轮播形式，而另一个版本使用的是单图形式。在这种情况下，Maria 测试的主要变量是什么？

Maria is conducting an A/B test to determine which ad format performs better. She is comparing a carousel ad format against a single image ad format. Therefore, the primary variable being tested is the ad format. The ad format is the specific creative structure used to present the ad content. The other options are incorrect because they represent different variables: Ad placement in the LinkedIn feed refers to where the ad appears, not its creative structure. The budget allocated to each campaign is a financial variable, not a creative one. Broad audience targeting settings relate to audience definition, not the ad's visual presentation.