Which built-in variable should you use to define an event trigger based on the class of a Submit button?

The Built-in Click Classes variable is the correct choice because it specifically captures the class attribute of the clicked element. Since you want to define an event trigger based on the class of the Submit button, this variable directly provides the necessary information for your trigger condition. The Built-in Event variable is a general variable that holds the name of the event (e.g., 'gtm.click'), not specific element attributes. The Built-in Element variable represents the entire HTML element that was clicked, not just its class. While you could potentially extract the class from it using custom JavaScript, the Click Classes variable is designed for this exact purpose. The Built-in Click Target variable captures the ID of the clicked element, which is different from its class.