The default execution mode for Databricks Auto Loader is Directory Listing. In this mode, Auto Loader identifies new files by periodically listing the input directory. This approach does not require additional cloud infrastructure setup (unlike the File Notification mode, which uses cloud-specific services). New files are loaded incrementally and idempotently into the target Delta Lake table. Option A describes File Notification mode (non-default), while Option B incorrectly implies querying all files (not incremental). Option C references webhooks and inferred rules, which are not part of Auto Loader. Option D correctly describes the default Directory Listing behavior.