Pressing CTRL+O is the correct answer because it is the keyboard shortcut for opening a file. The other options, CTRL+V, SHIFT+O, and CTRL+SHIFT+O, do not correspond to the action of opening a file. CTRL+V is the shortcut for pasting, SHIFT+O does not have a specific function, and CTRL+SHIFT+O is typically used for organizing bookmarks in some web browsers. Therefore, CTRL+O is the most appropriate shortcut for opening a file.