A. F1
B. F2
C. F3
D. F4
The F1 key is the keyboard shortcut to open the help menu for a program or Windows.
Explanation
The F1 key is a function key, which are the keys at the top of the keyboard labeled F1 through F12.
You can also use the Windows logo key + F1 to open Windows Help and Support.
In Microsoft Word, you can also use the Alt+Q shortcut to open the Tell Me or Search field on the ribbon to search for help content.
Related shortcuts
ALT+F4: Closes the Help window
ALT+TAB: Switches between the Help window and the active program
ALT+HOME: Goes back to the table of contents in PowerPoint Help and How-to
The correct answer to the question: "Which short cut key used for help ?" is "F1".