The yy key combination in the vi editor is used to copy the current line. The vi editor is an interactive, cryptic, and screen-based text editor used to create and edit a file. It operates in either Input mode or Command mode. In Input mode, the vi editor accepts a keystroke as text and displays it on the screen, whereas in Command mode, it interprets keystrokes as commands. As the vi editor is case sensitive, it interprets the same character or characters as different commands, depending upon whether the user enters a lowercase or uppercase character. When a user starts a new session with vi, he must put the editor in Input mode by pressing the "I" key. If he is not able to see the entered text on the vi editor's screen, it means that he has not put the editor in Insert mode. The user must change the editor to Input mode before entering any text so that he can see the text he has entered. Answer: D is incorrect. It deletes next char on the right. Answer: A is incorrect. It deletes the current line and one line above. Answer: C is incorrect. It deletes from the cursor till the end of the line.