If you'd like to restrict the number of screens within an activity that students can interact with at a given time, you can use Teacher Pacing. Simply click on the Teacher Pacing icon in the upper left hand corner of your screen within the teacher dashboard.
You will be prompted to choose the first and last screen that students will see. If you only want students to see a single screen, only select one screen. The pages that students will be able to freely access will be highlighted in orange.
Students will notice very little change on their screens apart from they will not be able to move backwards or forwards from the screens that you've selected. On the teacher dashboard, you'll see an orange display across the top that will alert you that teacher pacing mode is turned on.
You can disable teacher pacing by selecting Stop or change the selected screens with Edit. Clicking the additional symbol will extend the teacher pacing to the next screen.