Checkbox combination

I have a small problem that probably can be fixed easy. I have this form with many check boxes and when some are checked a text will appear in a movieclip. The code is like this:



Btn.onRelease = function() {


    if (checkb1.selected && checkb2.selected) {
        Mclip1.gotoAndStop(0);
        Mclip2.gotoAndStop(2);
        
    }
       
        else if (checkb3.selected) {
        Mclip1.gotoAndStop(0;
        Mclip2.gotoAndStop(3);
        }

else if (checkb1.selected && checkb2.selected && checkb3.selected) {
        Mclip1.gotoAndStop(0;
        Mclip2.gotoAndStop(4);
        }

Simple but when I add more combinations it wont work. For example when I have checkb1.selected && checkb3.selected && checkb5.selected it will react as if I checked checkb1 and checkb3.