function closecb () {
document.getElementById('contentbox1').style.display="none";
document.getElementById('contentbox2').style.display="none";
document.getElementById('contentbox3').style.display="none";
document.getElementById('contentbox4').style.display="none";
}

function showcb1() {
closecb();
document.getElementById('contentbox1').style.display="block";
}

function showcb2() {
closecb();
document.getElementById('contentbox2').style.display="block";
}
function showcb3() {
closecb();
document.getElementById('contentbox3').style.display="block";
}
function showcb4() {
closecb();
document.getElementById('contentbox4').style.display="block";
}