function change(x)
{
	document.getElementById('vol1').style.visibility="hidden";
	document.getElementById('vol2').style.visibility="hidden";
	document.getElementById('vol3').style.visibility="hidden";
	document.getElementById('vol4').style.visibility="hidden";

	switch (x)
	{
		case "1":
			document.getElementById('vol1').style.visibility="visible";
			break
		case "2":
			document.getElementById('vol2').style.visibility="visible";
			break
		case "3":
			document.getElementById('vol3').style.visibility="visible";
			break
		case "4":
			document.getElementById('vol4').style.visibility="visible";
			break
	}

}