To open the existing presentation, press A. Ctrl + L B. Ctrl + N C. Ctrl + A D. Ctrl + O

The correct answer is: D. Ctrl + O

To open an existing presentation in Microsoft PowerPoint, you can press the keyboard shortcut Ctrl+O. This will open the Open dialog box, where you can select the presentation you want to open.

The other options are not correct. Ctrl+L is used to open a new slide, Ctrl+N is used to create a new presentation, and Ctrl+A is used to select all text in a presentation.