For a prospect to re-enter a repeating Engagement Studio program, they must be removed from the recipient list after their first run and then added back. The most effective method is to use a static list. A form completion action adds the prospect to the static recipient list, starting their journey. A step within the program, placed just before the end, removes the prospect from that same list. This makes them eligible to be added again by the completion action when they resubmit the form, thus allowing them to repeat the program as intended.

B: This option is incomplete. While an automation rule can add prospects to a list, this method omits the crucial step of removing the prospect from the list, which is required for re-entry.

C: A dynamic list based on form completion is unsuitable for this repeating scenario. The prospect would permanently match the list's criteria after the first submission and would never be removed, thus preventing them from re-entering the program.

D: Using a trigger for the same action that adds a prospect to the recipient list is redundant. This approach also fails to include the necessary step of removing the prospect from the list to enable re-entry.

1. Salesforce Help, Account Engagement Documentation, "Considerations for Repeating Engagement Programs": This document explicitly states the requirement for re-entry: "To reenter a program, a prospect must be removed from the program’s recipient list and then added back to it." This supports the logic in answer A and directly contradicts the viability of answer C.

2. Salesforce Help, Account Engagement Documentation, "Engagement Program Action Steps": This page details the available "Action" steps within Engagement Studio, including "Remove from List," which is the mechanism used in the correct answer (A) to make a prospect eligible for re-entry.

3. Salesforce Help, Account Engagement Documentation, "Completion Actions": This resource confirms that "Add to List" is a standard completion action available on forms, which serves as the entry mechanism in the correct answer (A).

4. Salesforce Help, Account Engagement Documentation, "Dynamic Lists": This document explains that dynamic lists automatically manage membership based on criteria. For a "form was completed" criterion, a prospect would not be automatically removed, making the list unsuitable for this repeating program use case as described in option C.