try { 
document.execCommand('BackgroundImageCache', false, true); 
} catch(e) {} 


function select_hidden(){
var obj1 = document.getElementById("dt_1");
var elems = obj1.getElementsByTagName("select");
for (i = 0; i < elems.length; i++) {
elems[i].style.visibility = "hidden";
}
}
function select_display(){
var elems = document.getElementsByTagName("select");
for (i = 0; i < elems.length; i++) {
elems[i].style.visibility = "visible";
}
}