Explanation:

To retrieve a one-time list of attendees added to a specific Account Engagement campaign, the best approach is to use a segmentation rule. Segmentation rules allow for static list creation based on defined criteria, such as campaign membership. Unlike dynamic lists or automation rules, segmentation rules do not continuously update and are ideal for one-time tasks. They search the database and perform the action—here, creating a list of campaign participants. Dynamic lists are unsuitable because they update in real-time, and automation rules are used for ongoing processes, not one-time data pulls.