Great, thanks Gary for your detailed reply, I totally got your meaning of what you mentioned, yes when show Presenter Display and don't use Mirror Displays in display setting, the projector will show as an extended display, for example in right of the main screen in Macbook, what I want:
In Presenter Display and don't use Mirror Displays, I need the keynote slide in Presenter Display are exactly same with projector screen, that is to say 2 slides in 2 displays are in mirror, include the cursor. Since when I give a lecture to my students, it is better to use Presenter Display then I can see slide notes, and when I move cursor to point something in Macbook, I hope the cursor can move in Projector synchronously in mirror, if not I have to move the cursor into projector and then my sight have to move to projector too, but the projector is in my back you may know, this is very inconvenient I have to have my sight moved between Macbook and projector Back and forth. And this function in powerpoint is fine.(2 screens are exactly same and in mirror, all actions and shows are same and synchronized.)
Only 2 options I can choose if use Keynote:
1. use Mirror Displays in setting as you pasted, make "Mirror Displays" selected, and projector screens will be exactly same with macbook screen, but this can't use Presenter Display in keynote and I can't see slide notes.
2. Don't use Mirror Displays but make projector as a extended display, in this I can use Presenter Display in keynote but cursor can't be existed at same time in 2 screens. (PPT can do this function very well.)
What I need is Presenter Display and the cursor can exist at same time in mirror in 2 screens(Macbook screen and projector screen.)
Hope you understand my trouble now:)
Thanks for your patience.