What action should you take to apply the background to all slides in a presentation?

To apply the background to all slides in a presentation, the appropriate action is to use the button that is specifically labeled for this purpose, which is the apply to all button. When you select a background for your slides and wish to maintain consistency across the entire presentation, this function allows you to apply the chosen background uniformly to every slide. This ensures visual cohesion, which is important for professional presentations.

Using the apply to all button saves time and effort, as it eliminates the need to manually set the background for each slide individually. Other options, such as clicking the save button, may store your presentation but will not change the background on all slides. Clicking the OK button typically serves to confirm an action or a setting but does not inherently apply a background across multiple slides. Accessing the design tab allows for background modifications but does not automatically apply those changes to all slides unless followed by using the apply to all function.