flag = false;
function pldn1() {
if(flag) id1.style.visibilty = "hidden";
else id1.style.visibility = "visible";
     id2.style.visibility = "hidden";
     id3.style.visibility = "hidden";
flag = !flag;
}
flag = false;
function pldn2() {
if(flag) id2.style.visibilty = "hidden";
else id2.style.visibility = "visible";
     id3.style.visibility = "hidden";
     id1.style.visibility = "hidden";
flag = !flag;
}

flag = false;
function pldn3() {
if(flag) id3.style.visibilty = "hidden";
else id3.style.visibility = "visible";
     id1.style.visibility = "hidden";
     id2.style.visibility = "hidden";
flag = !flag;
}