What must be listed after the USING clause in an ABAP Managed database procedure?

The correct choice is to list ABAP Dictionary tables used in the procedure body after the USING clause in an ABAP Managed database procedure. This is essential because the USING clause explicitly defines which database tables the procedure has access to, thereby enhancing data security and integrity by limiting the scope of the procedure to only the necessary tables.

The USING clause acts as a mechanism for dependency management within the database procedure, ensuring that the procedure can only work with the defined tables which are structured and available in the ABAP Dictionary. This is crucial when creating procedures that interact with database objects since it allows for clearer documentation of the resources that the procedure will utilize and ensures that any changes in table definitions can be managed effectively.

In contrast, customer data tables, ABAP internal tables, and SAP GUI interfaces are not directly listed in the USING clause because they do not represent the structured database objects that are strictly managed in the database context as ABAP Dictionary tables do. Customer data can be found within ABAP Dictionary tables, but they're not specified separately in the USING clause. ABAP internal tables are runtime structures that reside in memory, while SAP GUI interfaces are related to the frontend interactions rather than database procedures, making them irrelevant to the USING clause.