function switch1(div) {
var option=['intro','one','two','three', 'three', 'four','five','six','seven','eight','nine','ten','eleven','twelve','thirteen','fourteen','fifteen','sixteen'];
for(var i=0; i<option.length; i++) {
if (document.getElementById(option[i])) {
obj=document.getElementById(option[i]);
obj.style.display=(option[i]==div)? "block" : "none";
}
}
}

window.onload=function () {switch1('intro');}