Answer : 4. "Ctrl + D"
Explanation :

1. In Microsoft PowerPoint, the Ctrl + D shortcut key inserts a duplicate of the selected slide.

2. Ctrl+D is a keyboard shortcut used in many computer programs to perform various tasks. In a web browser, pressing Ctrl+D adds the current webpage to your bookmarks or favourites list.

3. In Microsoft Excel and Google Sheets, pressing Ctrl+D fills a cell and overwrites it with the contents of the cell in a column above it.