How do you

Hi,
I am using the following code:

stop();
_root.c1._visible=false;
_root.c2._visible=false;
_root.c3._visible=false;
_root.c4._visible=false;
var checks=_root.c1 and _root.c2 and _root.c3 and _root.c4;
if (checks._visible=true) {
gotoAndStop (“congratulations”);
}
else {
gotoAndStop(“start”);
}

c1 through c4 are movieclips. They get revealed when a person clicks on the corresponding button. What I want to do is change the frame to “congratualtions” when all four C’s (c1, c2, c3, and c4) are visible. How do I do that?