What is the first step to add a subreport control in Design view?

To add a subreport control in Design view, the correct first step is to click on the "Subform/Subreport" button in the Controls group. This action is essential because it specifically activates the option to insert a subreport control into the current form or report. The "Subform/Subreport" button is designed for this purpose, allowing users to easily select and place a subreport in the intended location within the layout.

Other options refer to unrelated steps in the process of using the Access interface. For example, opening Backstage view via the "File" tab does not pertain to design choices in creating or modifying reports or forms. Similarly, selecting the "Use an existing report or form radio" button is a subsequent step that comes after initiating the subreport process, not a first step. Clicking the drop-down arrow in the Detail section might relate to accessing properties or parameters of a detail section but does not initiate adding a subreport control itself. Thus, focusing on the specific controls available in Design view is the appropriate approach to begin integrating subreports.